Fixes issue with missing overflow bubble

The problem had two parts:
1 When BubbleBarViewController removed all views, including the overflow
bubble, it did not update the value of the mOverflowAdded field
2 BubbleBarController removed all views upon receiving an initial update
This CL addresses both issues.

Test: Manual. Ensure the overflow bubble is present in the bubble bar.
Rotate the device and verify that the overflow bubble remains visible.
Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 380281090

Change-Id: I1810671e6bfc5b8b402433697b07f3de2e612ed7