Fix enter causing miscompletion of new project watches

Pressing Enter while completing a project name when adding a new
project to your watch list caused a server error with the partially
completed name displayed.  Work around it with the same solution
we used within d9a780a526f6649f863d1f118b4c8bc5a0d52cef, delaying
the submit until the completion is closed.

Bug: issue 507
Change-Id: I1efa776ae544e80254bbbc397af9106a458d8815
Signed-off-by: Shawn O. Pearce <sop@google.com>