Red Bug #1

After the last tab was deleted, typing into the new anonymous (untitled) tab set the change indicator and attempting to close the changed tab displayed querySave. If Save was chosen, no message was displayed and the querySave entered an endless loop.

Fixes
1. In tabShown, for tabs without a document, set trackChanges to false. Also set mode to text.
2. In SaveFile, if editor is readOnly or fpath is the empty string, end a querySave if one is running.

Only fix 1 was required. Fix 2 deals with a scenario which should no longer occur.