if (!(t = strchr (s, ':')))
if (!s || !(t = strchr (s, ':')))
url_scheme_t url_check_scheme (const char *s){  char sbuf[STRING];  char *t;  int i;    if (!(t = strchr (s, ':')))    return U_UNKNOWN;  if ((t - s) + 1 >= sizeof (sbuf))    return U_UNKNOWN;    strfcpy (sbuf, s, t - s + 1);  for (t = sbuf; *t; t++)    *t = ascii_tolower (*t);  if ((i = mutt_getvaluebyname (sbuf, UrlMap)) == -1)    return U_UNKNOWN;  else    return (url_scheme_t) i;}