MDEV-28747 Index condition pushdown may be configured incorrectly

ha_innobase::build_template may initialize m_prebuilt->idx_cond
even if there is no valid pushed_idx_cond_keyno.
This potentially problematic piece of code was found while
working on MDEV-27366

storage/innobase/handler/ha_innodb.cc

@@ -7718,9 +7718,12 @@ ha_innobase::build_template(
 
 	ulint num_v = 0;
 
-	if ((active_index != MAX_KEY
-	     && active_index == pushed_idx_cond_keyno)
-	    || (pushed_rowid_filter && rowid_filter_is_active)) {
+	if (active_index != MAX_KEY
+	     && active_index == pushed_idx_cond_keyno) {
+		m_prebuilt->idx_cond = this;
+		goto icp;
+	} else if (pushed_rowid_filter && rowid_filter_is_active) {
+icp:
 		/* Push down an index condition or an end_range check. */
 		for (ulint i = 0; i < n_fields; i++) {
 			const Field* field = table->field[i];
@@ -7901,9 +7904,6 @@ ha_innobase::build_template(
 				}
 			}
 		}
-		if (active_index == pushed_idx_cond_keyno) {
-			m_prebuilt->idx_cond = this;
-		}
 	} else {
 no_icp:
 		/* No index condition pushdown */