app: Don't reuse the GeglProcessor

Don't reuse the GeglProcessor as it can't handle dirty rects when
painting in GIMP, and this makes it harder to make GEGL-wise progress
in other parts of GIMP.

app/core/gimpprojection-construct.c

@@ -158,6 +158,12 @@ gimp_projection_construct_gegl (GimpProjection *proj,
     gegl_processor_set_rectangle (proj->processor, &rect);
 
   while (gegl_processor_work (proj->processor, NULL));
+
+  /* FIXME: Reuse it when it can handle dirty rects when painting
+   * properly
+   */
+  g_object_unref (proj->processor);
+  proj->processor = NULL;
 }
 
 static void