Fix Naga breaking unbreakable blocks (#128)

Author: ModularityEnjoyer

src/main/java/twilightforest/entity/boss/EntityTFNaga.java

@@ -623,8 +623,9 @@ protected void crumbleBelowTarget(int range) {
     protected void breakBlock(int dx, int dy, int dz) {
         Block whatsThere = worldObj.getBlock(dx, dy, dz);
         int whatsMeta = worldObj.getBlockMetadata(dx, dy, dz);
+        float whatsHardness = whatsThere.getBlockHardness(worldObj, dx, dy, dz);
 
-        if (whatsThere != Blocks.air) {
+        if ((whatsThere != Blocks.air) && (whatsHardness >= 0)) {
             whatsThere.dropBlockAsItem(worldObj, dx, dy, dz, whatsMeta, 0);
             this.worldObj.setBlock(dx, dy, dz, Blocks.air, 0, 2);