ShellUserVerifier: fix fail counter

If it is updated after checking, it counts the number of failures
not including the current one, so it allows one extra attempt. Instead,
by updating it before checking, we get the expected result of dropping the
curtain at the third password.

https://bugzilla.gnome.org/show_bug.cgi?id=687132

js/gdm/util.js

@@ -333,12 +333,11 @@ const ShellUserVerifier = new Lang.Class({
         // Otherwise, we allow ALLOWED_FAILURES attempts. After that, we
         // go back to the welcome screen.
 
+        this._failCounter++;
         let canRetry = retry && this._userName &&
             this._failCounter < this._settings.get_int(ALLOWED_FAILURES_KEY);
 
         if (canRetry) {
-            this._failCounter++;
-
             this.clear();
             this.begin(this._userName, new Batch.Hold());
         } else {