fix: isolate dispose on app exit handling

Author: NathanWalker

NativeScript/runtime/Runtime.mm

@@ -48,8 +48,10 @@
 
     Runtime::isolates_.erase(std::remove(Runtime::isolates_.begin(), Runtime::isolates_.end(), this->isolate_), Runtime::isolates_.end());
 
-    this->isolate_->Dispose();
-
+    if (![NSThread isMainThread]) {
+        this->isolate_->Dispose();
+    }
+    
     currentRuntime_ = nullptr;
 }