Fix missing "need eval data" for texpaint mode toggle op.

Note that am not sure that is actually needed, since switching to that
mode does not actually use any eval data, it's only needed during init
of first stroke... But in doubt, that won't hurt to have it here anyway.

source/blender/editors/sculpt_paint/paint_image.c

@@ -1166,7 +1166,7 @@ void PAINT_OT_texture_paint_toggle(wmOperatorType *ot)
 	ot->poll = texture_paint_toggle_poll;
 
 	/* flags */
-	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_USE_EVAL_DATA;
 }