Fix blank pink loading icons by ensuring that cache entry won't downgrade existing icon.

Bug: 326607598
Test: manually tested B&R
Flag: N/A
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d073ab0b3922eb0320a6bc2141cd4a57593a0cac)
Merged-In: I8aac643ec5ca3162cd62bf1051cc751800c626dd
Change-Id: I8aac643ec5ca3162cd62bf1051cc751800c626dd