Fixed an issue with font sizes between users

Because the user switching callback was posted,
the timing would be off, such that at inflation
time, the user wouldn't be switching, leading
to wrong font sizes in the wrong user.

Change-Id: Ied60acf0a8d1ebe7db18bdb1d786722d1efdcdfc
Fixes: 67507904
Test: switch between users with different font sizes