While in gimp mode only use darkroom

dt_view_manager_switch_by_view() is a noop if we are in "--gimp file" mode, there is no gimp error so far
and we are already in darkroom mode.

src/views/view.c

@@ -256,6 +256,11 @@ gboolean dt_view_manager_switch_by_view(dt_view_manager_t *vm,
   dt_view_t *old_view = vm->current_view;
   dt_view_t *new_view = (dt_view_t *)nv; // views belong to us, we can de-const them :-)
 
+  if(old_view
+      && !strcmp(dt_view_manager_name(vm), "Darkroom")
+      && dt_check_gimpmode("file")
+      && !darktable.gimp.error)
+    return FALSE;
   // reset the cursor to the default one
   dt_control_change_cursor(GDK_LEFT_PTR);