If glBlitFramebuffer tries to blit massive rectangles, it can result in
NaNs. This change ignores those rectangles instead of trying to blit
them.

Added a unittest for blitting a framebuffer.

Also fixed a typo in a debug message.

Bug chromium:979986

Change-Id: Ifd8e379f27b6882044bb93c6a68647b8474e7afc
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/34428
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Presubmit-Ready: Sean Risser <srisser@google.com>
Tested-by: Sean Risser <srisser@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>