Revert "remove unnecessary checks"

This reverts commit 309d660bbb.

src/uvw/async.cpp

@@ -16,8 +16,9 @@ UVW_INLINE int async_handle::init() {
 }
 
 UVW_INLINE void async_handle::send() {
-    // uv_async_send only returns an error if the handle has the wrong type which is not the case here
-    uv_async_send(raw());
+    if(auto err = uv_async_send(raw()); err != 0) {
+        publish(error_event{err});
+    }
 }
 
 } // namespace uvw