mlog: terminate a string at last char, just in case

contrib/epee/src/mlog.cpp

@@ -59,6 +59,7 @@ static std::string generate_log_filename(const char *base)
     strcpy(tmp, "unknown");
   else
     strftime(tmp, sizeof(tmp), "%Y-%m-%d-%H-%M-%S", &tm);
+  tmp[sizeof(tmp) - 1] = 0;
   filename += "-";
   filename += tmp;
   return filename;