Bug #46175: NULL read_view and consistent read assertion

The optimizer must not continue executing the current query
if e.g. the storage engine reports an error.
This is somewhat hard to implement with Item::val_xxx()
because they do not have means to return error code.
This is why we need to check the thread's error state after
a call to one of the Item::val_xxx() methods.

Fixed store_key_item::copy_inner() to return an error state 
if an error happened during the call to Item::save_in_field() 
because it calls Item::val_xxx().
Also added similar checks to related places.

sql/item.cc

@@ -5141,7 +5141,7 @@ int Item::save_in_field(Field *field, bool no_conversions)
     field->set_notnull();
     error=field->store(nr, unsigned_flag);
   }
-  return error;
+  return error ? error : (field->table->in_use->is_error() ? 2 : 0);
 }
 
 

sql/sql_select.h

@@ -709,6 +709,12 @@ class store_key_item :public store_key
     my_bitmap_map *old_map= dbug_tmp_use_all_columns(table,
                                                      table->write_set);
     int res= item->save_in_field(to_field, 1);
+    /*
+     Item::save_in_field() may call Item::val_xxx(). And if this is a subquery
+     we need to check for errors executing it and react accordingly
+    */
+    if (!res && table->in_use->is_error())
+      res= 2;
     dbug_tmp_restore_column_map(table->write_set, old_map);
     null_key= to_field->is_null() || item->null_value;
     return (err != 0 || res > 2 ? STORE_KEY_FATAL : (store_key_result) res); 
@@ -742,6 +748,12 @@ class store_key_const_item :public store_key_item
         if (!err)
           err= res;
       }
+      /*
+        Item::save_in_field() may call Item::val_xxx(). And if this is a subquery
+        we need to check for errors executing it and react accordingly
+        */
+      if (!err && to_field->table->in_use->is_error())
+        err= 2;
     }
     null_key= to_field->is_null() || item->null_value;
     return (err > 2 ?  STORE_KEY_FATAL : (store_key_result) err);