Fixed memory leak due to non-freed temporary PropList

When menus are read in the PropList format, they are loaded into a
temporary PropList object, which is parsed into the internal menu
structure, and the PropList object is no more used. There were two
cases where this temp object was not freed.

src/rootmenu.c

@@ -574,6 +574,9 @@ static WMenu *constructPLMenu(WScreen *screen, char *path)
 		return NULL;
 
 	menu = configureMenu(screen, pl, False);
+
+	WMReleasePropList(pl);
+
 	if (!menu)
 		return NULL;
 
@@ -1075,6 +1078,9 @@ static WMenu *readPLMenuPipe(WScreen * scr, char **file_name)
 		return NULL;
 
 	menu = configureMenu(scr, plist, False);
+
+	WMReleasePropList(plist);
+
 	if (!menu)
 		return NULL;