Mark last render target bound ID invalid after clearing texture levels using glClear

Fixes WebGL invalid framebuffer issues.

Change-Id: I841b8aa27f126feeb9971123c8b025630cdd3e0b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/241757
Commit-Queue: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed