Initialize static variable to make linter happy

Summary: Uninitialized variable defaults to 0 in this context. Make it explicit.

Test Plan: None. No functional change.

Reviewers: O1 Blessed Committers, speck

Reviewed By: O1 Blessed Committers, speck

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25470