Check for empty mpvecs in mpvec_garbage_collector()
Check for empty mpvecs in mpvec_garbage_collector()

During shutdown the mpvec pointer can indeed be empty, so we should
check it first before trying to access it.

References: 437245

Signed-off-by: Hannes Reinecke <b0d1e9e4a4e27620745ff49be9000da3174a4cc6@suse.de>

vijaychauhan/multipath-tools,grzn/multipath-tools-explained,unakatsuo/multipath-tools,grzn/multipath-tools-explained,gebi/multipath-tools,vijaychauhan/multipath-tools,unakatsuo/multipath-tools,unakatsuo/multipath-tools