Only call dismissCallback cancel on reset if bouncer is showing

There are many ways that reset() can get called, including coming
out of dozing. This has the potential to remove a registered
callback before the dismissal has actually occurred. The callback
should only be canceled if the user has closed the bouncer.

Fixes: 363091441
Test: atest StatusBarKeyguardViewManagerTest
Flag: EXEMPT bugfix
Change-Id: I3b8b55f7f1748433bdf7078dbf027076fc3f30b8