Fix bombing of submarines with mixed force

Fix bombing of submarines with mixed force

When bombing ships with a force containing both planes with and
without capability ASW, pin_bomb() could fail to report presence of
submarines, and could refuse to bomb ships when there were only
submarines.  The culprit is pin_bomb()'s check for capability ASW: it
checked whether the first plane in the plane list was capable instead
of checking whether any plane in the list was capable.