Avoids some edge cases that overflow or round incorrectly.

Fixes:
dEQP-GLES2.functional.state_query.floats.depth_range_getinteger
dEQP-GLES2.functional.state_query.floats.color_clear_value_getinteger
dEQP-GLES2.functional.state_query.floats.depth_clear_value_getinteger

Change-Id: Ib2c7f422dac76094c7ff6c5f8aef3fd392f68e80
Reviewed-on: https://chromium-review.googlesource.com/268510Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>