Fix null pointer exception rendering cubes widget

It turns out RemoteViews.fromFillinIntent(Intent) is incorrectly
marked as @Nonnull. Its caller RemoteViews.setOnClickFiilinIntent
does not require the intent to be non null. So guard the call to
collectExtraIntentKeys with a null check.

Bug: 402501535
Test: Manual
Flag: EXEMPT bugfix
Change-Id: I2c2d7a9a6c7b916aa988414db1f5e67997ee72ca