Fix texture formats that only require extensions failing requirements checks.
Fix texture formats that only require extensions failing requirements checks.

Unset version requirements equate to UINT_MAX causing requirements checks
for fail for formats that only need extensions such as DXT formats.

Fixes tests that require compressed formats.

Passes conformance/extensions/webgl-compressed-texture-s3tc.html

BUG=angleproject:884

Change-Id: Id810c477a359bf9d35a886c60735a91b51d1e931
Reviewed-on: https://chromium-review.googlesource.com/275693
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>
Tested-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

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