Now that the GLES unit tests can cause the float calculations in
these functions to result in inf and NaN, some platforms are throwing
errors when those floats are converted to integers. The Clip*Rect
functions no longer continue processing if any operation results in a
non-finite value, and tell their callers that they have failed to clip
properly.

Make Context.cpp set the error state to GL_INVALID_OPERATION when it
fails to blit.

Bug chromium:979986

Change-Id: I8e11e77b1e25eab37dee97aa616a908737b16036
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35269
Presubmit-Ready: Sean Risser <srisser@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Sean Risser <srisser@google.com>