Fix utf-8 char path in windows

The file 'E:\安安\scrcpy-win64-v1.12.1-1-g31bd950\scrcpy-server'
exists, however, it will show msg as follow:

    INFO: scrcpy 1.12.1 <https://github.com/Genymobile/scrcpy>
    stat: No such file or directory
    ERROR: 'E:\安安\scrcpy-win64-v1.12.1-1-g31bd950\scrcpy-server' does
    not exist or is not a regular file
    Press any key to continue...

This patch fixes it.

Signed-off-by: Yu-Chen Lin <npes87184@gmail.com>
Signed-off-by: Romain Vimont <rom@rom1v.com>

app/src/sys/win/command.c

@@ -4,6 +4,8 @@
 #include "util/log.h"
 #include "util/str_util.h"
 
+#include <sys/stat.h>
+
 static int
 build_cmd(char *cmd, size_t len, const char *const argv[]) {
     // Windows command-line parsing is WTF:
@@ -90,3 +92,22 @@ get_executable_path(void) {
     buf[len] = '\0';
     return utf8_from_wide_char(buf);
 }
+
+bool
+is_regular_file(const char *path) {
+    wchar_t *wide_path = utf8_to_wide_char(path);
+    if (!wide_path) {
+        LOGC("Could not allocate wide char string");
+        return false;
+    }
+
+    struct _stat path_stat;
+    int r = _wstat(wide_path, &path_stat);
+    SDL_free(wide_path);
+
+    if (r) {
+        perror("stat");
+        return false;
+    }
+    return S_ISREG(path_stat.st_mode);
+}