hwdec_cuda/vulkan: fix partial failure edge cases in error paths

[philipl]

These changes were inspired by the slopbot, but I went through and manually verified them, identifying additional problems, and better solutions along the way.

---

hwdec_cuda: fix partial failure edge cases in error paths

The slopbot spam did find valid issues in the error paths in this code, and as
part of verifying them, I have additional fixes.

• ensure that the return value -1 from cuda_init() if ext_init() fails
• zero alloc the ext_vk and ext_gl structs so that we have a known initial
  state
• explicitly initialise the sem_handle.fd to -1 to ensure we don't
  accidentally close stdin in the error path. But also don't do this on
  windows as an invalid Handle is 0.
• Don't do a double cuCtxPopCurrent() in the ext_gl init failure path

Fixes #17976, #17988, #17989

---

hwdec_vulkan: fix partial failure edge cases in error paths

This is another file where the slopbot identified a problem, but I was
surprised to see it fix it in a poor way and also miss an adjacement
problem.

mapper_map calls mapper_unmap with the intention of using it to clean
up partial failure after some planes are wrapped and released while others
are not. But the current code would actually segfault in that situation.

There are two fixes required:

• Ensure p->vkf is set by mapper_map early so that its available to
  mapper_unmap in the error path
• Don't call vkfc->unlock_frame in the mapper_map error path, as
  this will be called by mapper_unmap

Fixes #17977

---