cron: consume blanks in system crontabs before options

On system crontabs, multiple blanks are not being consumed after reading the
username. This change adds blank consumption before parsing any -[qn] options.
Without this change, an entry like:

  * * * * * username  -n true  # Two spaces between username and option.

will fail, as the shell will try to execute (' -n true'), while an entry like:

  * * * * * username -n true   # One space between username and option.

works as expected (executes 'true').

For user crontabs, this is not an issue as the preceding (day of week
or @shortcut) processing consumes any leading whitespace.

PR:		253699
Submitted by:	Eric A. Borisch <eborisch@gmail.com>
MFC after:	1 week

usr.sbin/cron/lib/entry.c

@@ -315,6 +315,9 @@ load_entry(file, error_func, pw, envp)
 			goto eof;
 		}
 
+		/* need to have consumed blanks when checking options below */
+		Skip_Blanks(ch, file)
+		unget_char(ch, file);
 #ifdef LOGIN_CAP
 		if ((s = strrchr(username, '/')) != NULL) {
 			*s = '\0';