The fuzzer found a crash where you can hit a DCHECK if you try to create a cursor from an empty bitmap, so I'm changing it to an early return, which is the normal error handling for this crash.
The fuzzer found a crash where you can hit a DCHECK if you try to create a cursor from an empty bitmap, so I'm changing it to an early return, which is the normal error handling for this crash.

BUG=573320

Review URL: https://codereview.chromium.org/1556153002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#367979}

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