Avoid unnecessary 'too late to disable compression' log warning

User has reported instances of log messages like the following after upgrading from 1.4.0 to 2.1.2:

2019-03-28 15:21:09.317707 I | http: multiple response.WriteHeader calls
2019-03-28T15:21:09.317-07:00 [WRN] EncodedResponseWriter: Too late to disableCompression! – rest.(*EncodedResponseWriter).disableCompression() at encoded_response_writer.go:63

It's not clear exactly what request is triggering this, but the code associated with the warning (EncodedResponseWriter.disableCompression) seems to suggest it could occur if disableCompression were called twice during the same request (which may align with the 'multiple response.WriteHeader calls' error).  Without additional repro steps, might require digging through the code to identify potential scenarios.