sofa registry service name conflict

have a look at
https://github.com/apache/dubbo/blob/56353aebc0c678582f7a2309dfd53d29b46deb3b/dubbo-registry/dubbo-registry-sofa/src/main/java/org/apache/dubbo/registry/sofa/SofaRegistry.java#L232-L246

conflict happens in following situation.
- first service:
version: v1, no group
- second service:
group: v1, no version

and both of them would have same service name like: com.dubbo.service:v1@dubbo.
it would be better if keep colon even version or group is empty.
e.g.
com.dubbo.service::v1
com.dubbo.service:v1:

@hengyunabc @ujjboy