Import Bug - No arguments are generated for stub methods when using `import` with proto definition

[huan]

If I'm using the import in the proto file, like the following:

https://github.com/huan/python-betterproto-issue/blob/60d232c90c099abca4aea6dc1273121cd4f43d66/proto_with_import/puppet_service.proto#L1-L9

Then the betterproto will fail to generate the argument of the Ding method, like this:

https://github.com/huan/python-betterproto-issue/blob/60d232c90c099abca4aea6dc1273121cd4f43d66/gen_proto_with_import/puppet_grpc.py#L13

As we are expecting this:

https://github.com/huan/python-betterproto-issue/blob/60d232c90c099abca4aea6dc1273121cd4f43d66/gen_proto_without_import/puppet_grpc.py#L21

Reproduce Repo at https://github.com/huan/python-betterproto-issue

[boukeversteegh]

Confirmed this bug and added a test-case f25c667