Adjusting texture completeness checks

Adjusting texture completeness checks

Mipmap levels used in texture sampling must be limited by the
texture's base level (default: 0) and max level (default: 1000).
This has an effect on texture completeness, since only the
required levels are required to be present in the texture to be
considered complete.

Change-Id: I31dd87d5a4306622e469c2546107b59f6e51c7dd
Reviewed-on: https://swiftshader-review.googlesource.com/4039
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>