Clear download link when new upload starts.

Bug: 32002078

Author: samtstern

storage/app/src/main/java/com/google/firebase/quickstart/firebasestorage/MainActivity.java

@@ -188,6 +188,10 @@ private void uploadFromUri(Uri fileUri) {
         // Save the File URI
         mFileUri = fileUri;
 
+        // Clear the last download, if any
+        updateUI(mAuth.getCurrentUser());
+        mDownloadUrl = null;
+
         // Toast message in case the user does not see the notificatio
         Toast.makeText(this, "Uploading...", Toast.LENGTH_SHORT).show();