grpc: Attempt to read trailers always when parsing grpc exception [DO NOT MERGE]

[DoumanAsh]

This should prevent missing grpc-status in case of inability to read message correctly

Unless this is changed, any failure to read body will result in generic IO exception when grpc-status is in trailers

[DoumanAsh]

I've been notified of #3087

Actually that makes sense if body read fails, but it doesn't make sense if body is just empty so I'm not sure if this PR is worth it

[oldergod]

Thanks for the PR. Do you think you could write a test in GrpcClientTest ?

[DoumanAsh]

Will do 👌

[DoumanAsh]

I tried to simulate situation that we encountered in wild but I think it doesn't go correctly through this part
https://github.com/square/wire/blob/master/wire-grpc-client/src/jvmMain/kotlin/com/squareup/wire/internal/RealGrpcCall.kt#L107-L109

For some reason even when I send empty body, it successfully passes despite exception supposed to be present
I'm not very familiar with internals but I guess this test suite doesn't simulate real client behavior

[DoumanAsh]

This is fundamentally not correct approach as trailers() might not be available due to how buggy okhttp library is
Correct approach would be to re-write grpc call to correctly handle empty response as distinct case instead of failing to read body

For reference: when trailers are not ready you would get exception

java.lang.IllegalStateException: too early; can't read the trailers yet