fix(tools): exclude unknown altitude from requested aircraft bands (#1115)

aircraft_in_area compared a nullable altitude, so a contact with neither barometric nor geometric altitude matched max_altitude_m as though it were at zero. Require a reported finite altitude only when a band is requested; unfiltered queries keep the contact.

changelog.d/1115-aircraft-altitude-band-unknown.md

@@ -0,0 +1,2 @@
+- Exclude aircraft without a reported altitude from requested altitude bands;
+  unfiltered aircraft queries still retain them (rudycelekli, #1115).