Fix a minor data race in PropertyInvalidatedCache

Ensure that the nonce value is set as part of its initialiation, within
the same lock scope. This ensures any pending reads that are waiting on
that initialization get the initial value.

Bug: 411728421
Test: presubmit
Flag: EXEMPT minor bugfix
Change-Id: Ibae17e14b762ca547e6ed321a903c07755078c95