Catch Bukkit-induced error in 1.7 - placeblock

Event is fired incorrectly every time... ignore it for now until Bukkit
fixes that.

src/main/java/net/aufdemrand/denizen/scripts/containers/core/WorldScriptHelper.java

@@ -225,6 +225,10 @@ public void blockBurn(BlockBurnEvent event) {
     @EventHandler
     public void blockCanBuild(BlockCanBuildEvent event) {
 
+        // TODO: Remove when Bukkit fixes error?
+        if (event.getMaterial() == null)
+            return;
+
         Map<String, dObject> context = new HashMap<String, dObject>();
         dMaterial oldMaterial = dMaterial.getMaterialFrom(event.getBlock().getType());
         dMaterial newMaterial = dMaterial.getMaterialFrom(event.getMaterial());