[CUDA] Make the new driver properly ignore non-CUDA inputs

The new driver generated offloadinga actions for each active toolchain.
However, for CUDA and HIP it is possible for the toolchain to be active
but one of the files is not a valid input. This can occur if the user
compiles both a CUDA and C source file in the same compiler invocation.
This patch adds some simple logic to quit if the input is not valid as
well.

Reviewed By: tra, MaskRay

Differential Revision: https://reviews.llvm.org/D129885