pmxcfs: status: remove superfluous NULL check

g_free can be passed a NULL pointer according to the docs [1], it does
nothing in that case.

[1] https://docs.gtk.org/glib/func.free.html

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>

src/pmxcfs/status.c

@@ -1562,9 +1562,7 @@ static void update_rrd_data(const char *key, gconstpointer data, size_t len) {
     }
 
 ret:
-    if (filename) {
-        g_free(filename);
-    }
+    g_free(filename);
 
     return;