fix: allow empty message on error objects

Specifically I was encountering errors of the form:

```json
{
  "name": "TimeoutError"
  "message": ""
}
```

being reported as invalid errors.

We really shouldn't require a message.

Author: birtles

src/to-exceptions.ts

@@ -81,7 +81,7 @@ function fromSimpleError(error: unknown): Error | null {
 
   const name = getStringMember('name') || getStringMember('errorClass');
   const message = getStringMember('message') || getStringMember('errorMessage');
-  if (!name || !message) {
+  if (!name) {
     return null;
   }