fix: Potential out of bounds access of flightmode name on main screen (#1337)

Take 2, without the Mac Companion breakage...

* fixed incorrect use of non-terminated-fixed-string for ctor of std::string

* introduced helper

* removed commented lines

* removed constexpr since in C++11 std::string ctro isn't still constexpr

Co-authored-by: wimalopaan <wilhelm.wm.meier@googlemail.com>

radio/src/gui/colorlcd/view_main_decoration.cpp

@@ -328,8 +328,8 @@ void ViewMainDecoration::createFlightMode()
   };
 
   std::function<std::string()> getFM = []() -> std::string {
-    return g_model.flightModeData[mixerCurrentFlightMode].name;
-  };
+      return stringFromNtString(g_model.flightModeData[mixerCurrentFlightMode].name);
+};
 
   flightMode = new DynamicText(this, r, getFM, CENTERED | COLOR_THEME_SECONDARY1);
 }