fixed file_close bug when file is NULL

include/tlibc/filesystem.h

@@ -59,6 +59,8 @@ str path_basename(str path, bool remove_ext);
 Result(FILE*) file_open(cstr file_name, cstr fopen_mode);
 
 static inline void file_close(FILE* f){
+    if(f == NULL)
+        return;
     fclose(f);
 }