Only uncollapse threads if there are replies

It doesn't make any sense to uncollapse threads which have no replies,
so bake this into the toggleCollapsed method of the ThreadController.

h/static/scripts/directives/test/thread-test.coffee

@@ -24,15 +24,22 @@ describe 'h:directives.thread', ->
         controller
 
     describe '#toggleCollapsed', ->
-      it 'toggles whether or not the thread is collapsed', ->
+      controller = null
+      count = null
+
+      beforeEach ->
         controller = createController()
+        count = sinon.stub().returns(0)
+        count.withArgs('message').returns(2)
+        controller.counter = {count: count}
+
+      it 'toggles whether or not the thread is collapsed', ->
         before = controller.collapsed
         controller.toggleCollapsed()
         after = controller.collapsed
         assert.equal(before, !after)
 
       it 'can accept an argument to force a particular state', ->
-        controller = createController()
         controller.toggleCollapsed(true)
         assert.isTrue(controller.collapsed)
         controller.toggleCollapsed(true)
@@ -42,6 +49,15 @@ describe 'h:directives.thread', ->
         controller.toggleCollapsed(false)
         assert.isFalse(controller.collapsed)
 
+      it 'does not allow uncollapsing the thread if there are no replies', ->
+        count.withArgs('message').returns(1)
+        controller.toggleCollapsed()
+        assert.isTrue(controller.collapsed)
+        controller.toggleCollapsed()
+        assert.isTrue(controller.collapsed)
+        controller.toggleCollapsed(false)
+        assert.isTrue(controller.collapsed)
+
     describe '#shouldShowAsReply', ->
       controller = null
       count = null

h/static/scripts/directives/thread.coffee

@@ -27,10 +27,16 @@ ThreadController = [
     # thread filter, if present.
     ###
     this.toggleCollapsed = (value) ->
-      @collapsed = if value?
-                     !!value
-                   else
-                     not @collapsed
+      newval = if value?
+                 !!value
+               else
+                 not @collapsed
+
+      # We only allow uncollapsing of the thread if there are some replies to
+      # display.
+      if newval == false and this.numReplies() <= 0
+        return
+      @collapsed = newval
 
     ###*
     # @ngdoc method