Fix Navigator jumpTo same route issue

Summary: facebook#8071 introduced a bug where jumping to the same navigator route would show a blank screen since the `index` check is not catching cases where the `transitionQueue` is empty.

Reviewed By: ericvicenti

Differential Revision: D3464697

fbshipit-source-id: 494527d1fb0ac5aea394abd3231dd19c56596549

Author: fred2028

Libraries/CustomComponents/Navigator/Navigator.js

@@ -373,9 +373,6 @@ var Navigator = React.createClass({
   },
 
   _transitionTo: function(destIndex, velocity, jumpSpringTo, cb) {
-    if (destIndex === this.state.presentedIndex && this.state.transitionQueue.length > 0) {
-      return;
-    }
     if (this.state.transitionFromIndex !== null) {
       this.state.transitionQueue.push({
         destIndex,
@@ -384,6 +381,9 @@ var Navigator = React.createClass({
       });
       return;
     }
+    if (destIndex === this.state.presentedIndex) {
+      return;
+    }
     this.state.transitionFromIndex = this.state.presentedIndex;
     this.state.presentedIndex = destIndex;
     this.state.transitionCb = cb;