Bug 1308631 - UpdateService: Do not apply update without update path. r=Grisha

Update path can be null. In this case we fallback to using the last saved path. However
if this doesn't exist either then we just continue with a null path and eventually crash
the service.

MozReview-Commit-ID: Kuihp496TEo

--HG--
extra : rebase_source : 96e2182571f4b2235b3fea25f449b2dbb3e17bb8

mobile/android/base/java/org/mozilla/gecko/updater/UpdateService.java

@@ -662,7 +662,10 @@ public class UpdateService extends IntentService {
         if (updatePath == null) {
             updatePath = getLastFileName();
         }
-        applyUpdate(new File(updatePath));
+
+        if (updatePath != null) {
+            applyUpdate(new File(updatePath));
+        }
     }
 
     private void applyUpdate(File updateFile) {