bomb launch interdiction: Fix crash on bombs missing target
plane damage() prints @noisy with snprintf() even when it's null. It
doesn't actually use the output then. Some systems (GNU, Windows)
deal gracefully with printing null strings, others crash. @noisy is
null when bombers or missiles miss and do collateral damage. Affects
bomb, launch, and interdiction missions. Broken in commit
820d755e5
"subs: Change pln_damage()'s parameter noisy to string prefix",
v4.3.33.
Fix by guarding the snprintf().
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>