Fix another CFStr reference leak

Fix another casw where the concatenation of result and str in name
creation doesn't release the source which is concated onto
result.

Sorry for two PRs here; the condition to tickle this is a bit
different than the condition to tickle the other.

RtMidi.cpp

@@ -1324,6 +1324,7 @@ CFStringRef CreateEndpointName( MIDIEndpointRef endpoint, bool isExternal )
   MIDIObjectGetStringProperty( endpoint, kMIDIPropertyName, &str );
   if ( str != NULL ) {
     CFStringAppend( result, str );
+    CFRelease(str);
   }
 
   // some MIDI devices have a leading space in endpoint name. trim