Default blocks to last asset instead of first

Author: paulkaplan

src/containers/blocks.jsx

@@ -340,9 +340,9 @@ class Blocks extends React.Component {
             const targetSounds = target.getSounds();
             const dynamicBlocksXML = this.props.vm.runtime.getBlocksXML();
             return makeToolboxXML(target.isStage, target.id, dynamicBlocksXML,
-                targetCostumes[0].name,
-                stageCostumes[0].name,
-                targetSounds.length > 0 ? targetSounds[0].name : ''
+                targetCostumes[targetCostumes.length - 1].name,
+                stageCostumes[stageCostumes.length - 1].name,
+                targetSounds.length > 0 ? targetSounds[targetSounds.length - 1].name : ''
             );
         } catch {
             return null;