changes to zdump.c and zic.c invocations of is.* macros

[Paul Eggert]

Arthur David Olson <olsona at elsie.nci.nih.gov> writes:

> ! 			if (isascii((unsigned char) *cp) &&
> ! 				isdigit((unsigned char) *cp))
> ! 					if (*cp++ == '1' &&
> ! 						*cp >= '0' && *cp <= '4')
> ! 							++cp;

Here's something that's a bit shorter, and perhaps simpler.

  if ('0' <= *cp && *cp <= '9' && *cp++ == '1' && '0' <= *cp && *cp <= '4')
    ++cp;

The C Standard guarantees that isdigit (ch) is equivalent to '0' <= ch
&& ch <= '9', and I don't know of any C implementation where that's
not true.

The above simplification could be done in two separate parts of the patch.