Ensure there is always at least one line if a empty document is created

lib/ace/document.js

@@ -46,6 +46,11 @@ var Document = function(text) {
 
     if (Array.isArray(text)) {
         this.insertLines(0, text);
+    }
+    // There has to be one line at least in the document. If you pass an empty
+    // string to the insert function, nothing will happen. Workaround.
+    else if (text.length == 0) {
+        this.$lines = [""];
     } else {
         this.insert({row: 0, column:0}, text);
     }

lib/ace/test/document_test.js

@@ -292,6 +292,11 @@ var Test = {
 
         doc.setValue(doc.getValue());
         assert.equal("1\n2", doc.getValue());
+    },
+
+    "test: empty document has to contain one line": function() {
+        var doc = new Document("");
+        assert.equal(doc.$lines.length, 1);
     }
 };