Fix assert when cleaning constraints in the transform tool

When enabled, the modal key item "Clear Constraint" did not reset
the default orientation.

This does not bring changes in the user's point of view.

source/blender/editors/transform/transform_constraints.c

@@ -976,6 +976,11 @@ void startConstraint(TransInfo *t)
 
 void stopConstraint(TransInfo *t)
 {
+  if (t->orient_curr != 0) {
+    t->orient_curr = 0;
+    transform_orientations_current_set(t, t->orient_curr);
+  }
+
   t->con.mode &= ~(CON_APPLY | CON_SELECT);
   *t->con.text = '\0';
   t->num.idx_max = t->idx_max;