The comparison used != which evaluates to NULL when the time entry has no
project, so entries that kept their task after the project was removed
were not reported.
Partial updates of time entries only validated end against start if both
were part of the payload. Start and end are now also validated against the
persisted value if only one of them is sent (fixes#1189).
The importers now fail if the end of a time entry is before the start and
the database consistency check reports such time entries.
