Bug 1224007 part 4. Fix some cases in which ErrorResult instances are destroyed without doing anything useful with exceptions on them. r=peterv

dom/html/HTMLMediaElement.cpp

@@ -2409,6 +2409,7 @@ HTMLMediaElement::WakeLockRelease()
   if (mWakeLock) {
     ErrorResult rv;
     mWakeLock->Unlock(rv);
+    rv.SuppressException();
     mWakeLock = nullptr;
   }
 }