Editor revisions start with 1, not 0.

There are some more problems in that area which are not addressed by
this patch. E.g. the synchronization of the AbstractEditorSupport
revision and the QTextDocument revision.

Task-number: QTCREATORBUG-11774
Change-Id: I4b0f41b2436ecedcd10dc0e3e39e5f185f990e05
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>