as the "Attempting to schedule tiles for bogus lon and lat = (-1000,0)"

bug happens now on a regular basis, and just ignoring it doesn't seem to
cause any harm, just return after it, rather than abort.

src/Scenery/tilemgr.cxx

@@ -163,6 +163,7 @@ void FGTileMgr::schedule_needed( double vis, const SGBucket& curr_bucket) {
         SG_LOG( SG_TERRAIN, SG_ALERT,
                 "Attempting to schedule tiles for bogus lon and lat  = ("
                 << longitude << "," << latitude << ")" );
+        return;		// FIXME
         SG_LOG( SG_TERRAIN, SG_ALERT,
                 "This is a FATAL error.  Exiting!" );
         exit(-1);