Emit 'item-added' before setting the ::activeItem when adding first item

Fixes atom/tabs#11

spec/pane-spec.coffee

@@ -44,11 +44,16 @@ describe "Pane", ->
       pane.addItem(item4)
       expect(pane.items).toEqual [item1, item2, item4, item3]
 
-    it "sets the active item if it is undefined", ->
+    it "sets the active item after adding the first item", ->
       pane = new Pane
       item = new Item("A")
+      events = []
+      pane.on 'item-added', -> events.push('item-added')
+      pane.$activeItem.changes.onValue -> events.push('active-item-changed')
+
       pane.addItem(item)
       expect(pane.activeItem).toBe item
+      expect(events).toEqual ['item-added', 'active-item-changed']
 
   describe "::activateItem(item)", ->
     pane = null

src/pane.coffee

@@ -132,8 +132,8 @@ class Pane extends Model
     return if item in @items
 
     @items.splice(index, 0, item)
-    @activeItem ?= item
     @emit 'item-added', item, index
+    @activeItem ?= item
     item
 
   # Public: Adds the given items to the pane.