Windows: fix fl_system() and fl_execvp() (STR 3438)

Use correct conversions to Windows "wide character" encoding and
use the appropriate wide character functions.

src/drivers/WinAPI/Fl_WinAPI_System_Driver.cxx

@@ -68,7 +68,7 @@ extern "C" {
 }
 
 /*
-  Convert a UTF-8 string to Windows wide character encoding (UTF-16).
+  Convert UTF-8 string to Windows wide character encoding (UTF-16).
 
   This helper function is used throughout this file to convert UTF-8
   strings to Windows specific UTF-16 encoding for filenames, paths, or
@@ -86,15 +86,14 @@ extern "C" {
   'wbuf' is NULL a new buffer is allocated with realloc(). Hence the pointer
   'wbuf' can be shared among multiple calls to this function if it has been
   initialized with NULL (or malloc or realloc) before the first call.
-  Ideally every call to this function has its own static pointer though.
 
   The return value is either the old value of 'wbuf' (if the string fits)
-  or a pointer at the (re)allocated buffer.
+  or a pointer to the (re)allocated buffer.
 
   Pseudo doxygen docs (static function intentionally not documented):
 
   param[in]     utf8    input string (UTF-8)
-  param[in,out] wbuf    in:  pointer to output string buffer
+  param[in,out] wbuf    in:  pointer to output string buffer or NULL
                         out: new string (the pointer may be changed)
   param[in]     lg      optional: input string length (default = -1)
 
@@ -227,43 +226,24 @@ FILE *Fl_WinAPI_System_Driver::fopen(const char *fnam, const char *mode) {
 }
 
 int Fl_WinAPI_System_Driver::system(const char *cmd) {
-# ifdef __MINGW32__
-  return ::system(fl_utf2mbcs(cmd));
-# else
   return _wsystem(utf8_to_wchar(cmd, wbuf));
-# endif
 }
 
 int Fl_WinAPI_System_Driver::execvp(const char *file, char *const *argv) {
-# ifdef __MINGW32__
+  int n = 0;
-  return _execvp(fl_utf2mbcs(file), argv);
+  while (argv[n]) n++; // count args
-# else
+  wchar_t **ar = (wchar_t **)calloc(sizeof(wchar_t *), n + 1);
-  wchar_t **ar;
+  // convert arguments first; trailing NULL provided by calloc()
+  for (int i = 0; i < n; i++)
+    ar[i] = utf8_to_wchar(argv[i], ar[i]); // alloc and assign
+  // convert executable file and execute it ...
   utf8_to_wchar(file, wbuf);
-
-  int i = 0, n = 0;
-  while (argv[i]) {i++; n++;}
-  ar = (wchar_t **)malloc(sizeof(wchar_t *) * (n + 1));
-  i = 0;
-  while (i <= n) {
-    unsigned wn;
-    unsigned len = (unsigned)strlen(argv[i]);
-    wn = fl_utf8toUtf16(argv[i], len, NULL, 0) + 1; // Query length
-    ar[i] = (wchar_t *)malloc(sizeof(wchar_t) * wn);
-    wn = fl_utf8toUtf16(argv[i], len, (unsigned short *)ar[i], wn); // Convert string
-    ar[i][wn] = 0;
-    i++;
-  }
-  ar[n] = NULL;
   _wexecvp(wbuf, ar);   // STR #3040
-  i = 0;
+  // clean up (reached only if _wexecvp() failed)
-  while (i < n) {
+  for (int i = 0; i < n; i++)
     free(ar[i]);
-    i++;
-  }
   free(ar);
   return -1;            // STR #3040
-#endif
 }
 
 int Fl_WinAPI_System_Driver::chmod(const char *fnam, int mode) {