Fix NULL reference in option parser

[000lbh]

If an option that needs an argument is given, but the argument is actually missing, the optind will increase by 1 and return, and if the option is the last option, a NULL reference occurs at setfont.c:290. This bug is fixed by returning '!' instead of '?' to main and process this condition separately.

[legionus]

@000lbh Yeah, you're right. But why not make it simpler and reduce optind if an argument is required?

--- a/src/setfont.c
+++ b/src/setfont.c
@@ -159,6 +159,7 @@ kbd_getopt(int argc, char **argv, const struct kbd_option *opts)
 
 required_argument:
        kbd_warning(0, "option '%s' requires an argument", name);
+       optind--;
        return '?';
 }
 

This will eliminate the need to create a new magic return code.

[000lbh]

Because this simple method will print two lines of warning: option %s requires an argument and invalid option %s. I think this is confusing, because here option %s is valid but with wrong number of arguments. May I add usage(EX_USAGE, opthelp) function call in function kbd_getopt after required_argument label instead to solve this problem, and this method will not create the new magic return code

Edited:
opthelp is local variable in main, so cannot be accessed in kbd_getopt. Maybe we need to make this variable global and static(to avoid symbol conflicts).

[legionus]

Because this simple method will print two lines of warning: option %s requires an argument and invalid option %s. I think this is confusing, because here option %s is valid but with wrong number of arguments.

I completely forgot about the second message. Yes, if it can be avoided, then it should be avoided. Your changes totally make sense. I'll apply it tomorrow.