Fixed BUG#4487: Stored procedure connection aborted if uninitialized char.

mysql-test/r/sp.result:
  New test case for BUG#4487.
mysql-test/t/sp.test:
  New test case for BUG#4487.
sql/item_func.h:
  Propagate null_value properly in sp functions.

mysql-test/r/sp.result

@@ -1820,6 +1820,19 @@ Ok
 Ok
 drop procedure bug5258|
 drop procedure bug5258_aux|
+create function bug4487() returns char
+begin
+declare v char;
+return v;
+end|
+Warnings:
+Warning	1311	Referring to uninitialized variable v
+select bug4487()|
+bug4487()
+NULL
+Warnings:
+Warning	1311	Referring to uninitialized variable v
+drop function bug4487|
 drop table if exists fac|
 create table fac (n int unsigned not null primary key, f bigint unsigned)|
 create procedure ifac(n int unsigned)

mysql-test/t/sp.test

@@ -1987,6 +1987,18 @@ call bug5258_aux()|
 drop procedure bug5258|
 drop procedure bug5258_aux|
 
+#
+# BUG#4487: Stored procedure connection aborted if uninitialized char
+#
+create function bug4487() returns char
+begin
+  declare v char;
+  return v;
+end|
+
+select bug4487()|
+drop function bug4487|
+
 
 #
 # Some "real" examples

sql/item_func.h

@@ -1130,25 +1130,31 @@ public:
   double val()
   {
     Item *it;
+    double d;
 
     if (execute(&it))
     {
       null_value= 1;
       return 0.0;
     }
-    return it->val();
+    d= it->val();
+    null_value= it->null_value;
+    return d;
   }
 
   String *val_str(String *str)
   {
     Item *it;
+    String *s;
 
     if (execute(&it))
     {
       null_value= 1;
       return NULL;
     }
-    return it->val_str(str);
+    s= it->val_str(str);
+    null_value= it->null_value;
+    return s;
   }
 
   void fix_length_and_dec();