BUG#15888454: SLAVE CRASHES WHEN DML REQUIRES CONVERSION & TABLE HAS

LESS COLUMNS THAN MASTER

Problem:
========
If DML operation requires a converstion at slave and if slave contains
less number of columns than master, slave is crashing.

Fix:
====
When Slave applies any DML operation, it sees if any of the columns 
requires conversion. If yes, it creates conversion table. 
While creating the coversion table, it should look into the actual number 
of columns required to create the table instead of getting the number
of columns from Master (size()). Columns would have dropped or added
at Slave. So the value should be min(columns@master, columns@slave)

sql/rpl_utility.cc:
  loop through only correct number of columns

sql/rpl_utility.cc

@@ -878,8 +878,13 @@ TABLE *table_def::create_conversion_table(THD *thd, Relay_log_info *rli, TABLE *
   DBUG_ENTER("table_def::create_conversion_table");
 
   List<Create_field> field_list;
-
-  for (uint col= 0 ; col < size() ; ++col)
+  /*
+    At slave, columns may differ. So we should create
+    min(columns@master, columns@slave) columns in the
+    conversion table.
+  */
+  uint const cols_to_create= min(target_table->s->fields, size());
+  for (uint col= 0 ; col < cols_to_create; ++col)
   {
     Create_field *field_def=
       (Create_field*) alloc_root(thd->mem_root, sizeof(Create_field));