Fix fuzzer-discovered error with SPIR-V interface arrays.

OSSFuzz discovered a minor variation of oss-fuzz:36770 which tickled a
different bug in SPIR-V RTFlip handling; we did not properly handle the
case where the InterfaceBlock is an array. SPIR-V does not support this
at all, but the IRGenerator allows it, and we don't detect it an an
error until later in the compilation process.

Change-Id: I80bd67a13dad878717dc122462132a2ed675532d
Bug: oss-fuzz:36850
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437018
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
4 files changed