iop/watermark: skip invalidation when disabled

The watermark module receives metadata and tag change signals in every darkroom session, even when it is disabled. Refreshing its pixelpipe cache and clearing mipmap_hash then causes unnecessary work and repeated thumbnail generation.

Ignore both signals while the module is disabled. This keeps enabled watermark text responsive to metadata changes while avoiding invalidation for other images.

Regression from #22103, unreleased.

Author: radialmonster

src/iop/watermark.c

@@ -1405,13 +1405,13 @@ static void _metadata_changed(gpointer instance,
                               const int type,
                               dt_iop_module_t *self)
 {
-  if(self) _invalidate_tag_meta(self);
+  if(self && self->enabled) _invalidate_tag_meta(self);
 }
 
 static void _tag_changed(gpointer instance,
                          dt_iop_module_t *self)
 {
-  if(self) _invalidate_tag_meta(self);
+  if(self && self->enabled) _invalidate_tag_meta(self);
 }
 
 void gui_init(dt_iop_module_t *self)