ssh: comment "fallthrough" in switch statement
Curl_pipeline_server_blacklisted: handle a NULL server name

Coverity CID 1215284. The server name is extracted with
Curl_copy_header_value() and passed in to this function, and
copy_header_value can actually can fail and return NULL.
curl_multi_remove_handle: remove dead code

Coverify CID 1157776. Removed a superfluous if() that always evaluated
true (and an else clause that never ran), and then re-indented the
function accordingly.
Curl_debug: document switch fallthroughs
parse_proxy: remove dead code.

Coverity CID 982331.