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

video/out/hwdec/hwdec_cuda.c

@@ -193,8 +193,10 @@ static int mapper_init(struct ra_hwdec_mapper *mapper)
         return ret;
 
     for (int n = 0; n < desc.num_planes; n++) {
-        if (!p_owner->ext_init(mapper, desc.planes[n], n))
+        if (!p_owner->ext_init(mapper, desc.planes[n], n)) {
+            ret = -1;
             goto error;
+        }
     }
 
  error:

video/out/hwdec/hwdec_cuda_gl.c

@@ -39,9 +39,8 @@ static bool cuda_ext_gl_init(struct ra_hwdec_mapper *mapper,
     struct cuda_mapper_priv *p = mapper->priv;
     CudaFunctions *cu = p_owner->cu;
     int ret = 0;
-    CUcontext dummy;
 
-    struct ext_gl *egl = talloc_ptrtype(NULL, egl);
+    struct ext_gl *egl = talloc_zero_ptrtype(NULL, egl);
     p->ext[n] = egl;
 
     struct ra_tex_params params = {
@@ -84,7 +83,6 @@ static bool cuda_ext_gl_init(struct ra_hwdec_mapper *mapper,
     return true;
 
 error:
-    CHECK_CU(cu->cuCtxPopCurrent(&dummy));
     return false;
 }
 

video/out/hwdec/hwdec_cuda_vk.c

@@ -55,9 +55,14 @@ static bool cuda_ext_vk_init(struct ra_hwdec_mapper *mapper,
     int mem_fd = -1;
     int ret = 0;
 
-    struct ext_vk *evk = talloc_ptrtype(NULL, evk);
+    struct ext_vk *evk = talloc_zero_ptrtype(NULL, evk);
     p->ext[n] = evk;
 
+#if !HAVE_WIN32_DESKTOP
+    // need to initialise fd as invalid; zero alloc covers the Win32 .handle
+    evk->sem_handle.fd = -1;
+#endif
+
     pl_gpu gpu = ra_pl_get(mapper->ra);
 
     struct pl_tex_params tex_params = {
@@ -163,8 +168,10 @@ static bool cuda_ext_vk_init(struct ra_hwdec_mapper *mapper,
     ret = CHECK_CU(cu->cuImportExternalSemaphore(&evk->cuda_sem, &w_desc));
     if (ret < 0)
         goto error;
+#if !HAVE_WIN32_DESKTOP
     // CUDA takes ownership of an imported FD *but not* an imported Handle.
     evk->sem_handle.fd = -1;
+#endif
 
     return true;