Fix for setting Toolbar content descriptions

Allow resid 0 as a null content description.

Change-Id: I0663feac229a77d5efffece2bd686de4ee99d840

core/java/android/widget/Toolbar.java

@@ -592,7 +592,7 @@ public class Toolbar extends ViewGroup {
      */
     public void setNavigationContentDescription(int resId) {
         ensureNavButtonView();
-        mNavButtonView.setContentDescription(getContext().getText(resId));
+        mNavButtonView.setContentDescription(resId != 0 ? getContext().getText(resId) : null);
     }
 
     /**