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);
 }

radio/src/strhelpers.h

@@ -25,6 +25,8 @@
 #include "definitions.h"
 #include "opentx_types.h"
 
+#include <string>
+
 #define SHOW_TIME  0x1
 #define SHOW_TIMER 0x0
 #define SHOW_TIMER_UPPER_CASE   0x2
@@ -90,4 +92,8 @@ char *getTimerString(int32_t tme, TimerOptions timerOptions = {.options = 0});
 void splitTimer(char *s0, char *s1, char *s2, char *s3, int tme,
                 bool bLowercase = true);
 
+template<size_t N>
+std::string stringFromNtString(const char (&a)[N]) {
+    return std::string(a, strnlen(a, N));        
+}    
 #endif  // _STRHELPERS_H_