Fix crash when passing wrong arguments.
Fix crash when passing wrong arguments.

THROW() did not actually throw in exception-enabled builds, silly
oversight.

h3xl3r/SPIRV-Cross,h3xl3r/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,h3xl3r/SPIRV-Cross,KhronosGroup/SPIRV-Cross,h3xl3r/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,h3xl3r/SPIRV-Cross