Fixed crash in SuggestionDialogFragment

Crash on (un)subscribe idea, when user closes suggestion dialog too fast, before server response was handled,
thus, in suggestionSubscriptionUpdated() getActivity() returns null => unhandled NullPointerException takes place.
Manifest declares minSdkVersion=8, but API level 11 was used without check in ArticleDialogFragment

WebView.onPause() introduced in API level 11