There are two conflicting requirements here:

- if there was an invalidation event, and PaintTile() is called due to
  that, then we're not interested in invalidation events generated by
  PaintTile() itself.
- we do want other event types all the time like the cursor rectangle

Change SwViewShell::libreOfficeKitCallback(), so that it doesn't ignore
all callbacks when we're in the callback already, just the so far only
problematic type: tile invalidation.

Change-Id: Idcaedbbe0fe2b5b1aa9bafbfe33a81c8011fe148