Don't decompress gzip data in http_client::download()

When using C++REST SDK, don't transparently decompressed gzip-compressed
content if it is application/octet-stream. Only do that for other
content types, typically JSON.

macOS implementation already behaves this way natively.

src/http_client_casablanca.cpp

@@ -89,6 +89,9 @@ class gzip_compression_support : public http::http_pipeline_stage
 
         return next_stage()->propagate(request).then([](http::http_response response) -> pplx::task<http::http_response>
         {
+            if (response.headers().content_type() == _XPLATSTR("application/octet-stream"))
+                return pplx::task_from_result(response); // don't try to decompress binary data
+
             string_t encoding;
             if (response.headers().match(http::header_names::content_encoding, encoding) && encoding == _XPLATSTR("gzip"))
             {