Fix the NPE issue in the Internet Settings

- Missing to remove the mRemoveLoadingRunnable in the onStop() function, which will cause the callback to run after the fragment is destroyed and encounter this NPE issue.

Bug: 193405782
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=NetworkProviderSettingsTest

Change-Id: I48b85173db1e6689dd056ba71f2fac776ffabbc9
2 files changed