wIconUpdate wwin checks

The variable wwin is only used in one block of the if, so should be moved
inside this block. OTOH, is better check if the variabl exists before
assign it. The code now is more stable and avoid crashes.

src/icon.c

@@ -599,11 +599,14 @@ static void unset_icon_image(WIcon *icon)
 
 void wIconUpdate(WIcon *icon, RImage *image)
 {
-	WWindow *wwin = icon->owner;
+	WWindow *wwin = NULL;
 
 	if (image) {
 		icon->file_image = image;
 	} else {
+		if (icon && icon->owner)
+			wwin = icon->owner;
+
 		if (wwin && WFLAGP(wwin, always_user_icon)) {
 			/* Forced use user_icon */
 			get_rimage_icon_from_user_icon(icon);