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/unix/command.c

@@ -15,6 +15,7 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <sys/types.h>
+#include <sys/stat.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
@@ -127,3 +128,14 @@ get_executable_path(void) {
     return NULL;
 #endif
 }
+
+bool
+is_regular_file(const char *path) {
+    struct stat path_stat;
+
+    if (stat(path, &path_stat)) {
+        perror("stat");
+        return false;
+    }
+    return S_ISREG(path_stat.st_mode);
+}