Some dEQP tests were not made for SPV_ENV_VULKAN_1_1, and error in the optimizer.
This produces 0 words of SPIR-V, that then goes and explodes in SpirvShader.

Add an assert to catch the 0-word case.

Bug: b/127454276
Change-Id: I60576e6691a9cf74656dfcd9c53aeed7ab578de1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/26188Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>