Fix GCC 10.2.0 -Og -Wmaybe-uninitialized

Fix some more cases after merging
commit 31aef3ae.
Some warnings look possibly genuine, others are clearly bogus.

sql/ha_partition.cc

 /*
   Copyright (c) 2005, 2019, Oracle and/or its affiliates.
-  Copyright (c) 2009, 2019, MariaDB
+  Copyright (c) 2009, 2020, MariaDB
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -6380,7 +6380,7 @@ ha_rows ha_partition::multi_range_read_info(uint keyno, uint n_ranges,
 {
   uint i;
   handler **file;
-  ha_rows rows;
+  ha_rows rows= 0;
   DBUG_ENTER("ha_partition::multi_range_read_info");
   DBUG_PRINT("enter", ("partition this: %p", this));
 
@@ -9516,7 +9516,6 @@ double ha_partition::read_time(uint index, uint ranges, ha_rows rows)
 
 ha_rows ha_partition::records()
 {
-  int error;
   ha_rows tot_rows= 0;
   uint i;
   DBUG_ENTER("ha_partition::records");
@@ -9525,9 +9524,10 @@ ha_rows ha_partition::records()
        i < m_tot_parts;
        i= bitmap_get_next_set(&m_part_info->read_partitions, i))
   {
-    ha_rows rows;
-    if (unlikely((error= m_file[i]->pre_records()) ||
-                 (rows= m_file[i]->records()) == HA_POS_ERROR))
+    if (unlikely(m_file[i]->pre_records()))
+      DBUG_RETURN(HA_POS_ERROR);
+    const ha_rows rows= m_file[i]->records();
+    if (unlikely(rows == HA_POS_ERROR))
       DBUG_RETURN(HA_POS_ERROR);
     tot_rows+= rows;
   }

sql/item_strfunc.cc

 /*
    Copyright (c) 2000, 2017, Oracle and/or its affiliates.
-   Copyright (c) 2009, 2019, MariaDB Corporation
+   Copyright (c) 2009, 2020, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -646,7 +646,7 @@ String *Item_func_concat_operator_oracle::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
   THD *thd= current_thd;
-  String *res;
+  String *res= NULL;
   uint i;
 
   null_value=0;
@@ -656,7 +656,7 @@ String *Item_func_concat_operator_oracle::val_str(String *str)
     if ((res= args[i]->val_str(str)))
       break;
   }
-  if (i == arg_count)
+  if (!res)
     goto null;
 
   if (res != str)

sql/sql_repl.cc

@@ -374,11 +374,15 @@ static int send_file(THD *thd)
     We need net_flush here because the client will not know it needs to send
     us the file name until it has processed the load event entry
   */
-  if (unlikely(net_flush(net) || (packet_len = my_net_read(net)) == packet_error))
+  if (unlikely(net_flush(net)))
   {
+  read_error:
     errmsg = "while reading file name";
     goto err;
   }
+  packet_len= my_net_read(net);
+  if (unlikely(packet_len == packet_error))
+    goto read_error;
 
   // terminate with \0 for fn_format
   *((char*)net->read_pos +  packet_len) = 0;

sql/sql_yacc.yy

@@ -4451,9 +4451,11 @@ sp_fetch_list:
             LEX *lex= Lex;
             sp_head *sp= lex->sphead;
             sp_pcontext *spc= lex->spcont;
-            sp_variable *spv;
+            sp_variable *spv= likely(spc != NULL)
+              ? spc->find_variable(&$1, false)
+              : NULL;
 
-            if (unlikely(!spc || !(spv = spc->find_variable(&$1, false))))
+            if (unlikely(!spv))
               my_yyabort_error((ER_SP_UNDECLARED_VAR, MYF(0), $1.str));
 
             /* An SP local variable */
@@ -4465,9 +4467,11 @@ sp_fetch_list:
             LEX *lex= Lex;
             sp_head *sp= lex->sphead;
             sp_pcontext *spc= lex->spcont;
-            sp_variable *spv;
+            sp_variable *spv= likely(spc != NULL)
+              ? spc->find_variable(&$3, false)
+              : NULL;
 
-            if (unlikely(!spc || !(spv = spc->find_variable(&$3, false))))
+            if (unlikely(!spv))
               my_yyabort_error((ER_SP_UNDECLARED_VAR, MYF(0), $3.str));
 
             /* An SP local variable */

sql/sql_yacc_ora.yy

@@ -4205,9 +4205,10 @@ sp_fetch_list:
             LEX *lex= Lex;
             sp_head *sp= lex->sphead;
             sp_pcontext *spc= lex->spcont;
-            sp_variable *spv;
-
-            if (unlikely(!spc || !(spv = spc->find_variable(&$1, false))))
+            sp_variable *spv= likely(spc != NULL)
+              ? spc->find_variable(&$1, false)
+              : NULL;
+            if (unlikely(!spv))
               my_yyabort_error((ER_SP_UNDECLARED_VAR, MYF(0), $1.str));
 
             /* An SP local variable */
@@ -4219,9 +4220,10 @@ sp_fetch_list:
             LEX *lex= Lex;
             sp_head *sp= lex->sphead;
             sp_pcontext *spc= lex->spcont;
-            sp_variable *spv;
-
-            if (unlikely(!spc || !(spv = spc->find_variable(&$3, false))))
+            sp_variable *spv= likely(spc != NULL)
+              ? spc->find_variable(&$3, false)
+              : NULL;
+            if (unlikely(!spv))
               my_yyabort_error((ER_SP_UNDECLARED_VAR, MYF(0), $3.str));
 
             /* An SP local variable */