Handle failure in ffi_closure_alloc

`ffi_closure_alloc` may fail and return `NULL` if, for instance, we're
running in a locked-down operating system that forbids FFI from
allocating executable pages of memory in any of the ways that it tries.
Today we pass this `NULL` on to `ffi_prep_closure_loc` which triggers a
segmentation fault that takes down the whole JVM. With this change we
check for a failure in this call and turn it into an
`UnsupportedOperationException` so that the caller can handle it more
gracefully.

Relates elastic/elasticsearch#73309
Relates elastic/elasticsearch#18272

CHANGES.md

@@ -11,6 +11,7 @@ Features
 
 Bug Fixes
 ---------
+* [#TBD](https://github.com/java-native-access/jna/pull/TBD): Handle failure in `ffi_closure_alloc` - [@davecturner](https://github.com/davecturner).
 
 
 Release 5.9.0

native/dispatch.c

@@ -3466,6 +3466,11 @@ Java_com_sun_jna_Native_registerMethod(JNIEnv *env, jclass UNUSED(ncls),
   }
 
   closure = ffi_closure_alloc(sizeof(ffi_closure), &code);
+  if (closure == NULL) {
+    throwByName(env, EUnsupportedOperation, "Failed to allocate closure");
+    status = FFI_BAD_ABI;
+    goto cleanup;
+  }
   status = ffi_prep_closure_loc(closure, closure_cif, dispatch_direct, data, code);
   if (status != FFI_OK) {
     throwByName(env, EError, "Native method linkage failed");