Fix T74657: Grease Pencil Proportional Editing does not work for

'Individual Origins'

Note gpencil doesnt do anything fancy like meshes in
editmesh_islands_info_calc(), but it looks like there is actually no
harm in allowing proportional editing with individual origins & gpencil
editmode.

Maniphest Tasks: T74657

Differential Revision: https://developer.blender.org/D7351

source/blender/editors/transform/transform.c

@@ -77,7 +77,7 @@ static void initSnapSpatial(TransInfo *t, float r_snap[3]);
 
 bool transdata_check_local_islands(TransInfo *t, short around)
 {
-  return ((around == V3D_AROUND_LOCAL_ORIGINS) && ((ELEM(t->obedit_type, OB_MESH))));
+  return ((around == V3D_AROUND_LOCAL_ORIGINS) && ((ELEM(t->obedit_type, OB_MESH, OB_GPENCIL))));
 }
 
 /* ************************** SPACE DEPENDENT CODE **************************** */