additional comment explaining helper function

Author: ianbotsf

aws-crt-kotlin/native/src/aws/sdk/kotlin/crt/http/HttpClientConnectionNative.kt

@@ -194,6 +194,7 @@ private fun dereferenceUserdata(userdata: COpaquePointer?): StableRef<HttpStream
     try {
         userdata?.asStableRef<HttpStreamContext>()
     } catch (_: NullPointerException) {
+        // `asStableRef()` can throw `NullPointerException` when target type can't be coerced to HttpStreamContext
         null
     }