IDEA-168069 Join Lines throws array index out of bonds on an empty file

platform/lang-impl/src/com/intellij/codeInsight/editorActions/JoinLinesHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2014 JetBrains s.r.o.
+ * Copyright 2000-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -142,6 +142,8 @@ public class JoinLinesHandler extends EditorActionHandler {
                                      @NotNull PsiFile psiFile,
                                      int startLine,
                                      Ref<Integer> caretRestoreOffset) {
+    if (startLine >= doc.getLineCount() - 1) return;
+
     docManager.doPostponedOperationsAndUnblockDocument(doc);
     docManager.commitDocument(doc);
     CharSequence text = doc.getCharsSequence();