Fix memory leak reported by Coverity

As reported in CID #331577, we re-use the variable 'tmp' without freeing
the previously allocated pointer.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

src/rootmenu.c

@@ -673,9 +673,13 @@ static void constructMenu(WMenu * menu, WMenuEntry * entry)
 
 				tmp = wexpandpath(path[i]);
 
-				if (strstr(tmp, "#usergnusteppath#") == tmp)
+				if (strstr(tmp, "#usergnusteppath#") == tmp) {
+					char *old_tmp = tmp;
+
 					tmp = wstrconcat(wusergnusteppath(),
 							  tmp + 17);
+					wfree(old_tmp);
+				}
 
 				wfree(path[i]);
 				lpath = getLocalizedMenuFile(tmp);