Fix compiler warning.

Kevin Gritter reports that his compiler complains about inq and outq
being possibly-uninitialized at the point where they are passed to
shm_mq_attach().  They are initialized by the call to
setup_dynamic_shared_memory, but apparently his compiler is inlining
that function and then having doubts about whether the for loop will
always execute at least once.  Fix by initializing them to NULL.