Fix issue preventing launcher from unblocking UI thread

When using a hardware bitmap in a paint that's being filtered, the
lazy-generated image was being incorrectly added to mMutableImages
which would then fail to pin. The failure to pin would be treated
as cache exhaustion, preventing the unblocking of the UI thread

Test: perfetto trace of launcher
Flag: EXEMPT bugfix
Change-Id: I1aceae0fb5a379f93f9991713b7b4975ef8bbd7e