Fix GCC 10.2.0 -Og -Wmaybe-uninitialized

sql/opt_range.cc

@@ -7555,13 +7555,15 @@ SEL_TREE *Item_bool_func::get_full_func_mm_tree(RANGE_OPT_PARAM *param,
   table_map param_comp= ~(param->prev_tables | param->read_tables |
 		          param->current_table);
 #ifdef HAVE_SPATIAL
-  Field::geometry_type sav_geom_type;
-  const bool geometry= field_item->field->type() == MYSQL_TYPE_GEOMETRY;
-  if (geometry)
+  Field::geometry_type sav_geom_type= Field::GEOM_GEOMETRY, *geom_type=
+    field_item->field->type() == MYSQL_TYPE_GEOMETRY
+    ? &(static_cast<Field_geom*>(field_item->field))->geom_type
+    : NULL;
+  if (geom_type)
   {
-    sav_geom_type= ((Field_geom*) field_item->field)->geom_type;
+    sav_geom_type= *geom_type;
     /* We have to be able to store all sorts of spatial features here */
-    ((Field_geom*) field_item->field)->geom_type= Field::GEOM_GEOMETRY;
+    *geom_type= Field::GEOM_GEOMETRY;
   }
 #endif /*HAVE_SPATIAL*/
 
@@ -7592,9 +7594,9 @@ SEL_TREE *Item_bool_func::get_full_func_mm_tree(RANGE_OPT_PARAM *param,
   }
 
 #ifdef HAVE_SPATIAL
-  if (geometry)
+  if (geom_type)
   {
-    ((Field_geom*) field_item->field)->geom_type= sav_geom_type;
+    *geom_type= sav_geom_type;
   }
 #endif /*HAVE_SPATIAL*/
   DBUG_RETURN(ftree);