Lazy strike at last call to xstrdup from garmin.cc

I'm not proud of this. Maybe daylight will bring me back to leaving the last caller out in another way.

garmin.h

@@ -112,7 +112,7 @@ class GarminFormat : public Format
 
   /* Data Members */
 
-  const char* portname{};
+  QString portname;
   MakeShort* mkshort_handle{};
   GPS_PWay* tx_waylist{};
   GPS_PWay* tx_routelist{};