genapts850: make sure we do not hang forever in a parse loop

when there are actually no airports to parse within the bounding box

src/Airports/GenAirports850/main.cxx

@@ -394,19 +394,21 @@ int main(int argc, char **argv)
         position = scheduler->FindAirport( start_id );
 
         // add remaining airports within boundary
-        scheduler->AddAirports( position, min_lat, min_lon, max_lat, max_lon );
-
+        if ( scheduler->AddAirports( position, min_lat, min_lon, max_lat, max_lon ) )
+        {
             // parse all the airports that were found
             scheduler->Schedule( num_threads, summary_file );
         }
+    }
     else
     {
         // find all airports within given boundary
-        scheduler->AddAirports( 0, min_lat, min_lon, max_lat, max_lon );
-
-        // and parser them
+        if ( scheduler->AddAirports( 0, min_lat, min_lon, max_lat, max_lon ) )
+        {
+            // and parse them
             scheduler->Schedule( num_threads, summary_file );
         }
+    }
 
     SG_LOG(SG_GENERAL, SG_INFO, "Done");
     exit(0);

src/Airports/GenAirports850/scheduler.cxx

@@ -590,7 +590,7 @@ void Scheduler::RetryAirport( AirportInfo* pai )
     retryList.push_back( *pai );        
 }
 
-void Scheduler::AddAirports( long start_pos, float min_lat, float min_lon, float max_lat, float max_lon )
+bool Scheduler::AddAirports( long start_pos, float min_lat, float min_lon, float max_lat, float max_lon )
 {
     char 	 line[2048];
     char*	 def;
@@ -760,6 +760,15 @@ void Scheduler::AddAirports( long start_pos, float min_lat, float min_lon, float
     	    }
     	}
 	}
+
+	// did we add airports to the parse list?
+        if ( originalList.size() )
+        {
+            return true;
+        } else
+        {
+            return false;
+        }
 }
 
 Scheduler::Scheduler(string& cmd, string& datafile, const string& root, const string_list& elev_src)

src/Airports/GenAirports850/scheduler.hxx

@@ -176,7 +176,7 @@ public:
 
     long            FindAirport( string icao );
     void            AddAirport(  string icao );
-    void            AddAirports( long start_pos, float min_lat, float min_lon, float max_lat, float max_lon );
+    bool            AddAirports( long start_pos, float min_lat, float min_lon, float max_lat, float max_lon );
     void            RetryAirport( AirportInfo* pInfo );
 
     void            Schedule( int num_threads, string& summaryfile );