possible leaks in add_file function

[joey.cheng]

There is no fclose after fopen for file variable.

fflush(file);
//fclose(file)<===missing!!
VLOG_F(g_internal_verbosity, "Logging to '" LOGURU_FMT(s) "', mode: '" LOGURU_FMT(s) "', verbosity: " LOGURU_FMT(d) "", path, mode_str, verbosity);
return true;