Fix UB when reporting out-of-range values.

It's undefined behavior to cast a double to an int64 if the double is
out of range. Our SkSL error tests managed to trigger UBSAN on the tree,
pinpointing the issue (which we had already written up a bug for).

Change-Id: Ia06896732223ff310f2c175efcbeb96ba5786fa8
Bug: skia:12863
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/505678
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
2 files changed