MDEV-35680 Table number > MAX_TABLES causes overflow of table_map at main.join test

Fix a regression introduced by commit d98ac85 (MDEV-29935, MDEV-26247) causing
MAX_TABLES overflow in `setup_table_map()`. The check for MAX_TABLES was moved
outside of the loop that increments table numbers, allowing overflows during
loop iterations. Since setup_table_map() operates on a 64-bit bitmap, table
numbers exceeding 64 triggered the UBSAN check.
This commit returns the overflow check within the loop and adds a debug
assertion to `setup_table_map()` to ensure no bitmap overrun occurs.

Author: Olernov

sql/sql_base.cc

@@ -7862,11 +7862,15 @@ bool setup_tables(THD *thd, Name_resolution_context *context,
           DBUG_RETURN(1);
       }
       tablenr++;
-    }
-    if (tablenr > MAX_TABLES)
-    {
-      my_error(ER_TOO_MANY_TABLES,MYF(0), static_cast<int>(MAX_TABLES));
-      DBUG_RETURN(1);
+      /*
+        Test MAX_TABLES overflow here inside the loop as setup_table_map()
+        called in each iteration is sensitive for this
+      */
+      if (tablenr > MAX_TABLES)
+      {
+        my_error(ER_TOO_MANY_TABLES, MYF(0), static_cast<int>(MAX_TABLES));
+        DBUG_RETURN(1);
+      }
     }
     if (select_insert && !is_insert_tables_num_set)
     {

sql/sql_base.h

@@ -353,6 +353,7 @@ inline void setup_table_map(TABLE *table, TABLE_LIST *table_list, uint tablenr)
     table->maybe_null= embedding->outer_join;
     embedding= embedding->embedding;
   }
+  DBUG_ASSERT(tablenr <= MAX_TABLES);
   table->tablenr= tablenr;
   table->map= (table_map) 1 << tablenr;
   table->force_index= table_list->force_index;