Minor fixes

Making sure LayerAdapter doesn't wait for ThangType to load the image more than once.
LayerAdapter skips rendering if there's a prerendered sprite sheet whose image is not loaded.

app/lib/surface/LayerAdapter.coffee

@@ -179,7 +179,8 @@ module.exports = LayerAdapter = class LayerAdapter extends CocoClass
       @listenToOnce(thangType, 'raster-image-loaded', @somethingLoaded)
       @numThingsLoading++
     else if prerenderedSpriteSheet = thangType.getPrerenderedSpriteSheetToLoad()
-      prerenderedSpriteSheet.loadImage()
+      startedLoading = prerenderedSpriteSheet.loadImage()
+      return if not startedLoading
       @listenToOnce(prerenderedSpriteSheet, 'image-loaded', -> @somethingLoaded(thangType))
       @numThingsLoading++
 
@@ -353,6 +354,8 @@ module.exports = LayerAdapter = class LayerAdapter extends CocoClass
 
   renderSegmentedThangType: (thangType, colorConfig, actionNames, spriteSheetBuilder) ->
     prerenderedSpriteSheet = thangType.getPrerenderedSpriteSheet(colorConfig, 'segmented')
+    if prerenderedSpriteSheet and not prerenderedSpriteSheet.loadedImage
+      return
     containersToRender = thangType.getContainersForActions(actionNames)
     spriteBuilder = new SpriteBuilder(thangType, {colorConfig: colorConfig})
     for containerGlobalName in containersToRender
@@ -377,6 +380,8 @@ module.exports = LayerAdapter = class LayerAdapter extends CocoClass
     prerenderedSpriteSheet = thangType.getPrerenderedSpriteSheet(colorConfig, 'singular')
     prerenderedFramesMap = {}
     if prerenderedSpriteSheet
+      if not prerenderedSpriteSheet.loadedImage
+        return
       scale = @resolutionFactor / (prerenderedSpriteSheet.get('resolutionFactor') or 1)
       for frame, i in prerenderedSpriteSheet.spriteSheet._frames
         sprite = new createjs.Sprite(prerenderedSpriteSheet.spriteSheet)

app/models/ThangType.coffee

@@ -541,8 +541,8 @@ class PrerenderedSpriteSheet extends CocoModel
   @className: 'PrerenderedSpriteSheet'
 
   loadImage: ->
-    return if @loadingImage or @loadedImage
-    return unless imageURL = @get('image')
+    return false if @loadingImage or @loadedImage
+    return false unless imageURL = @get('image')
     @image = $("<img src='/file/#{imageURL}' />")
     @loadingImage = true
     @image.one('load', =>
@@ -554,6 +554,7 @@ class PrerenderedSpriteSheet extends CocoModel
       @loadingImage = false
       @trigger('image-load-error', @)
     )
+    return true
 
   buildSpriteSheet: ->
     @spriteSheet = new createjs.SpriteSheet({