Prevent division by zero in FairQueueing when no active pipes are available

This commit fixes a potential DivideByZeroException in the FairQueueing class by conditionally performing the modulo operation only when there are active pipes (m_active > 0). This issue occurs during round-robin processing of messages when all pipes have been deactivated. The modification ensures stability and prevents crashes under these specific conditions.

Author: fales-in-wonderland

src/NetMQ/Core/Patterns/Utils/FairQueueing.cs

@@ -122,7 +122,7 @@ public bool RecvPipe(ref Msg msg, [NotNullWhen(returnValue: true)] out Pipe? pip
 
                     m_more = msg.HasMore;
                     if (!m_more)
-                        m_current = (m_current + 1) % m_active;
+                        m_current = m_active > 0 ? (m_current + 1) % m_active : 0;
                     return true;
                 }