Insure onLoadRequest only waits for correct number of listeners.

Fixes #3157

When GeckoView started short cutting onLoadRequest, the number of
Navigation Listeners would be larger when the GeckoRequest was finally
processed so the GeckoResult would never get completed and the load
would never start.

app/src/common/shared/org/mozilla/vrbrowser/browser/engine/Session.java

@@ -1004,14 +1004,15 @@ public void onCanGoForward(@NonNull GeckoSession aSession, boolean aCanGoForward
         final GeckoResult<AllowOrDeny> result = new GeckoResult<>();
         AtomicInteger count = new AtomicInteger(0);
         AtomicBoolean allowed = new AtomicBoolean(false);
+        final int listenerCount = mNavigationListeners.size() - 1;
         for (GeckoSession.NavigationDelegate listener: mNavigationListeners) {
             GeckoResult<AllowOrDeny> listenerResult = listener.onLoadRequest(aSession, aRequest);
             if (listenerResult != null) {
                 listenerResult.then(value -> {
                     if (AllowOrDeny.ALLOW.equals(value)) {
                         allowed.set(true);
                     }
-                    if (count.getAndIncrement() == mNavigationListeners.size() - 1) {
+                    if (count.getAndIncrement() == listenerCount) {
                         result.complete(allowed.get() ? AllowOrDeny.ALLOW : AllowOrDeny.DENY);
                     }
 
@@ -1020,7 +1021,7 @@ public void onCanGoForward(@NonNull GeckoSession aSession, boolean aCanGoForward
 
             } else {
                 allowed.set(true);
-                if (count.getAndIncrement() == mNavigationListeners.size() - 1) {
+                if (count.getAndIncrement() == listenerCount) {
                     result.complete(allowed.get() ? AllowOrDeny.ALLOW : AllowOrDeny.DENY);
                 }
             }