GP: Add Fill keyframe if active not equal to CFRA

When fill a stroke if the fill layer hasn't keyframe, the fill is wrong because previous fill shape hide area to fill.

Now, if the keyframe is missing in the active layer for the current frame, a new frame is added.

source/blender/editors/gpencil/gpencil_fill.c

@@ -220,6 +220,13 @@ static void gp_draw_datablock(tGPDfill *tgpf, const float ink[4])
 		if (gpl->flag & GP_LAYER_HIDE)
 			continue;
 
+		/* if active layer and no keyframe, create a new one */
+		if (gpl == tgpf->gpl) {
+			if (gpl->actframe->framenum != cfra_eval) {
+				BKE_gpencil_layer_getframe(gpl, cfra_eval, GP_GETFRAME_ADD_NEW);
+			}
+		}
+
 		/* get frame to draw */
 		bGPDframe *gpf = BKE_gpencil_layer_getframe(gpl, cfra_eval, GP_GETFRAME_USE_PREV);
 		if (gpf == NULL)