Delete the readers and writers (which closes them automatically) to prevent memory leaks.

simgear/io/SGDataDistributionService.cxx

@@ -274,10 +274,10 @@ bool
 SG_DDS::close()
 {
     for (auto it : readers)
-        it->close();
+        delete it;
 
     for (auto it : writers)
-        it->close();
+        delete it;
 
     readers.clear();
     writers.clear();

simgear/io/SGDataDistributionService.hxx

@@ -67,7 +67,7 @@ public:
     }
 
     /** Destructor */
-    ~SG_DDS_Topic();
+    virtual ~SG_DDS_Topic();
 
     // Set the paramaters which weren't available at creation time and use
     // a custom topic name.