DocumentsUI: Handle NPE gracefully

Cherry-picked from OmniROM.

http://jira.omnirom.org/browse/OMNI-956

Change-Id: I8d50d71a9c91486dfc9e5da01538c6b5a626f054
DocumentsUI: Remove catch-all statements

This removes several "catch (Exception)" statements which violates the Android code
style guidelines and hides problems.

I left some catch-all statements in, as they seem to be intended like this (grep for
"catch (Exception").

I suggest we do not merge this before we are sure that we fixed any problems. One problem
is a crash when deleting items (I'm currently working to fix that).

PS 2: Add exception to log.
Change-Id: I483c320c7ee256acd993dd2a509c031fa5e3f09e