memset arrays in TestForPreservingPMConversions in case of read pixels failure

Bug: chromium:837649
Change-Id: Iced3cef5af8745964323ef3fa8cc5ac9d184c3b4
Reviewed-on: https://skia-review.googlesource.com/124350
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed