fix: Fix bug with missing token in latex folding (#5093)

* fix bug with missing token

* add test for latex folding

Issue #5090

src/mode/folding/latex.js

@@ -63,7 +63,7 @@ oop.inherits(FoldMode, BaseFoldMode);
 
         var getType = function() {
             var token = stream.stepForward();
-            var type = token.type == "lparen" ?stream.stepForward().value : "";
+            var type = token && token.type == "lparen" ? stream.stepForward().value : "";
             if (dir === -1) {
                 stream.stepBackward();
                 if (type)

src/mode/folding/latex_test.js

@@ -0,0 +1,31 @@
+if (typeof process !== "undefined") require("amd-loader");
+
+"use strict";
+
+var LatexMode = require("../latex").Mode;
+var EditSession = require("../../edit_session").EditSession;
+var assert = require("../../test/assertions");
+
+module.exports = {
+    "test: latex block folding": function () {
+        var session = new EditSession([
+            '\\usepackage{amsmath}', '\\title{\\LaTeX}', '\\date{}', '\\begin'
+        ]);
+
+        var mode = new LatexMode();
+        session.setFoldStyle("markbegin");
+        session.setMode(mode);
+
+        assert.equal(session.getFoldWidget(0), "");
+        assert.equal(session.getFoldWidget(1), "");
+        assert.equal(session.getFoldWidget(2), "");
+        assert.equal(session.getFoldWidget(3), "start");
+        assert.equal(session.getFoldWidgetRange(3), null);
+
+        session.setValue(session.getValue() + '{test}\nsome text here \n\\end{test}');
+
+        assert.range(session.getFoldWidgetRange(3), 3, 12, 5, 0);
+    }
+};
+
+if (typeof module !== "undefined" && module === require.main) require("asyncjs").test.testcase(module.exports).exec();