Avoid SK_ABORT in sksl-minify when code does not compile.

If you are running sksl-minify directly, this gives a slightly nicer
user experience. Previously it reported the error, but since it was
using SK_ABORT, it looked kind of like a crash.

Change-Id: I26968f3f301f2f47179961ef8b6ba1901649bc0e
Bug: skia:13822
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/595679
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed