Limit color space xform formats to the valid range in fuzzing

There are only 7 ColorFormat values.

Bug: chromium:842483
Change-Id: I92e10ed9147b8df607fd5ea62e9a0a5f2300c14c
Reviewed-on: https://chromium-review.googlesource.com/1057452Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
Cr-Commit-Position: refs/heads/master@{#558351}

testing/libfuzzer/fuzzers/skia_color_space_fuzzer.cc

@@ -37,8 +37,8 @@ static void ColorTransform(size_t hash, bool input) {
 
   static uint32_t output[kPixels * 4];
 
-  const auto form1 = SkColorSpaceXform::ColorFormat(hash >> 0 & 7);
-  const auto form2 = SkColorSpaceXform::ColorFormat(hash >> 3 & 7);
+  const auto form1 = SkColorSpaceXform::ColorFormat((hash >> 0) % 7);
+  const auto form2 = SkColorSpaceXform::ColorFormat((hash >> 3) % 7);
   const auto alpha = SkAlphaType(hash >> 6 & 3);
 
   transform->apply(form1, output, form2, pixels, kPixels, alpha);