Fix Division by Zero in FairQueueing when m_active is 0

[fales1488]

Problem

As detailed in issue #1088, the FairQueueing class in NetMQ is prone to a DivideByZeroException when all inbound pipes are deactivated and m_active becomes zero. This issue occurs during the round-robin selection process in the RecvPipe method.

Solution

This pull request implements a conditional check to ensure that the modulo operation for round-robin scheduling is only performed when there is at least one active pipe (m_active > 0). This change prevents the system from attempting a division by zero, which can lead to an application crash under specific scenarios.

Changes Made

• Modified the round-robin index update line in RecvPipe method to:

  
  if (!m_more)
    m_current = m_active > 0 ? (m_current + 1) % m_active : 0;