lima: increase epsilon for depthrange near == far

For some specific values of depthrange, the exception for handling near == far doesn't seem to work by only decreasing 'near' by 1 unit. Increase the difference by also incrementing the 'far' distance in this case, to avoid artifacts in applications doing that.

I don't know how good practice that is from a GL standpoint, but the application seems to work everywhere else but in lima, so we should probably fix it.

Fixes #4492 (closed)

More debug notes in #4492 (comment 857961)

No changes in deqp/piglit.