con.c: Reorder use after free

This shows up in various static analysis tools. I doubt that it is dangerous in any way but the end result is the same.

src/con.c

@@ -91,8 +91,8 @@ void con_free(Con *con) {
         FREE(mark->name);
         FREE(mark);
     }
-    free(con);
     DLOG("con %p freed\n", con);
+    free(con);
 }
 
 static void _con_attach(Con *con, Con *parent, Con *previous, bool ignore_focus) {