Fix SkParse::FindNamedColor OOB

Plus some minor cleanup and asserts.

Bug: oss-fuzz:23395

Change-Id: I667bee2d7f21864defe2fd97df9eb4e99d69d9ca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296451
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Tyler Denniston <tdenniston@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
diff --git a/gn/tests.gni b/gn/tests.gni
index 5b8b99f..d8b7494 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -185,6 +185,7 @@
   "$_tests/PaintImageFilterTest.cpp",
   "$_tests/PaintTest.cpp",
   "$_tests/ParametricStageTest.cpp",
+  "$_tests/ParseColorTest.cpp",
   "$_tests/ParsePathTest.cpp",
   "$_tests/PathCoverageTest.cpp",
   "$_tests/PathMeasureTest.cpp",