Only remove the '\n' at the end of a line if there is one.

I missed this as part of the fix to the PR below.

PR:		31265
Submitted by:	Matthew D. Fuller <fullermd@over-yonder.net>
MFC after:	1 week

usr.sbin/cron/lib/misc.c

@@ -392,7 +392,8 @@ in_file(string, file)
 	rewind(file);
 	while (fgets(line, MAX_TEMPSTR, file)) {
 		if (line[0] != '\0')
-			line[strlen(line)-1] = '\0';
+			if (line[strlen(line)-1] == '\n')
+				line[strlen(line)-1] = '\0';
 		if (0 == strcmp(line, string))
 			return TRUE;
 	}