TCI - Handle null oldDiagnostic in applyValidation

Incremental UI updates for incremental re-validation of the
model did not handle the case where the VDiagnostic is
created for the first time after the view listener is already
attached, which makes the oldDiagnostic null and results in
an NPE on attempt to get its list of diagnostics.

Change-Id: I3538a4cee61324574510cd344c85e8f3e36a92e5
Signed-off-by: Christian W. Damus <give.a.damus@gmail.com>
3 files changed