BUG/MEDIUM: mux-fcgi: reject stream ID 0 for application records

BUG/MEDIUM: mux-fcgi: reject stream ID 0 for application records

Records with a stream ID set to 0 are reserved to management records.
However there was no check to trigger an error if an application record is
received with a stream ID to 0. This could lead to crash becausqe management
streams (which are static and immutable) can be modified while processing
application records (STDOUT/STDERR/END_REQUEST).

To fix the issue, An error is returned if the stream ID 0 is set on
GET_VALUES_RESULT or UNKNOWN_TYPE records.

This patch must be backported to all stable versions.