Fix displaying of file diff if draft patch has been deleted

Displaying any file diff for a patch set fails if the change has any
gaps in its patch set history. Patch sets can be missing, if they
have been drafts and were deleted. In this case displaying a file diff
fails because an IndexOutOfBoundsException occurs when setting the
style for the patch set link of the active patch set.

Bug: issue 1555
Change-Id: Ib63e4082e27f184b4092baa08a84d89bb7932346
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchSetSelectBox.java

diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchSetSelectBox.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchSetSelectBox.java
index 5d4207f..afaf7fd 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchSetSelectBox.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchSetSelectBox.java
@@ -35,8 +35,8 @@
 import com.google.gwt.user.client.ui.Image;
 import com.google.gwtorm.client.KeyUtil;
 
-import java.util.LinkedList;
-import java.util.List;
+import java.util.HashMap;
+import java.util.Map;
 
 public class PatchSetSelectBox extends Composite {
   interface Binder extends UiBinder<HTMLPanel, PatchSetSelectBox> {
@@ -63,7 +63,7 @@
   PatchSet.Id idActive;
   Side side;
   PatchScreen.Type screenType;
-  List<Anchor> links;
+  Map<Integer, Anchor> links;
 
   @UiField
   HTMLPanel linkPanel;
@@ -88,7 +88,7 @@
     this.idSideA = idSideA;
     this.idSideB = idSideB;
     this.idActive = (side == Side.A) ? idSideA : idSideB;
-    this.links = new LinkedList<Anchor>();
+    this.links = new HashMap<Integer, Anchor>();
 
     linkPanel.clear();
 
@@ -105,7 +105,7 @@
       baseLink = createLink(PatchUtil.C.patchBase(), null);
     }
 
-    links.add(baseLink);
+    links.put(0, baseLink);
     if (screenType == PatchScreen.Type.UNIFIED || side == Side.A) {
       linkPanel.add(baseLink);
     }
@@ -117,7 +117,7 @@
     for (Patch patch : script.getHistory()) {
       PatchSet.Id psId = patch.getKey().getParentKey();
       Anchor anchor = createLink(Integer.toString(psId.get()), psId);
-      links.add(anchor);
+      links.put(psId.get(), anchor);
       linkPanel.add(anchor);
     }