[FIX] GUI, HTML parsing, availability check

Author: ChristianGruen

basex-core/src/main/java/org/basex/build/html/HtmlParser.java

@@ -324,7 +324,7 @@ static void ensureAvailable(final String className, final byte[] func,
     /**
      * Returns the parser associated with the specified HTML options.
      * @param options HTML options.
-     * @return parser
+     * @return parser (can be {@code null})
      */
     public static Parser of(final HtmlOptions options) {
       return of(options, Parser.DEFAULT);

basex-core/src/main/java/org/basex/gui/dialog/DialogHtmlParser.java

@@ -37,15 +37,15 @@ final class DialogHtmlParser extends DialogParser {
     hopts = new HtmlOptions(opts.get(MainOptions.HTMLPARSER));
 
     final Parser parser = Parser.of(hopts);
-    final boolean avl = parser.available(hopts);
+    final boolean available = parser != null && parser.available(hopts);
 
     options = new BaseXTextField(dialog, hopts.toString());
     options.setToolTipText(tooltip(hopts));
     info = new BaseXLabel(" ").border(12, 0, 6, 0);
 
     final BaseXBack pp  = new BaseXBack(new RowLayout(8));
-    pp.add(new BaseXLabel(avl ? Util.info(H_HTML_PARSER_X, parser) : H_NO_HTML_PARSER));
-    if(avl) {
+    pp.add(new BaseXLabel(available ? Util.info(H_HTML_PARSER_X, parser) : H_NO_HTML_PARSER));
+    if(available) {
       final BaseXBack p = new BaseXBack(new ColumnLayout(8));
       p.add(new BaseXLabel(PARAMETERS + COL, true, true));
       p.add(options);