fix(worker): report a worker's __runOnMainThread exception without its isolate handle

The exception a worker's callback threw kept a handle into the worker isolate after RunMainThreadEntry let go of it, so the isolate could be disposed before the event loop reported it, and the report resolved the handle against the main thread's isolate. For a worker's callback the exception now drops the handle while the isolate is still held, and only its message and stack reach Java.

Author: adrian-niculescu

test-app/runtime/src/main/cpp/CallbackHandlers.cpp

@@ -772,8 +772,15 @@ void CallbackHandlers::RunMainThreadEntry(uint64_t key) {
 
     if (tc.HasCaught() &&
         !NativeScriptException::ContainUncaughtCallbackException(isolate, tc)) {
+        NativeScriptException ex(tc);
+        if (!runtime->IsMainThread()) {
+            // Reported only after this function lets go of the isolate, which
+            // its worker may dispose by then, and from the main thread, which
+            // never enters it: only the message and stack can travel.
+            ex.ReleaseJsHandle();
+        }
         // surfaces via the event loop's guard as a pending Java exception
-        throw NativeScriptException(tc);
+        throw ex;
     }
 }