[script] Accept labels on lines terminated with CRLF

CRLF line terminators are allowed in scripts; the carriage return is
simply interpreted as trailing whitespace and so is ignored.  This
fails on lines containing script labels, since the label-finding code
checks for a line containing only the ":" marker and the label itself
(without any trailing whitespace).

Fix by allowing a label to be terminated by either a NUL or a
whitespace character.

Reported-by: Bovey Christian <Christian.Bovey@chuv.ch>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/image/script.c

  * @ret rc		Return status code
  */
 static int goto_find_label ( const char *line ) {
+	size_t len = strlen ( goto_label );
 
 	if ( line[0] != ':' )
 		return -ENOENT;
-	if ( strcmp ( goto_label, &line[1] ) != 0 )
+
+	if ( strncmp ( goto_label, &line[1], len ) != 0 )
+		return -ENOENT;
+
+	if ( line[ 1 + len ] && ! isspace ( line[ 1 + len ] ) )
 		return -ENOENT;
+
 	return 0;
 }