Check for a valid ProxyCache in ResourceCache::purgeResources

The ProxyCache isn't always allocated so check before accessing it.

Bug: chromium:1477795
Change-Id: I762d4f3d450a9a27ede284a6abc70645632020f9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/750717
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
1 file changed