SPIGOT-5500: Lectern cannot be replaced using /setblock and other commands

nms-patches/BlockLectern.patch

@@ -0,0 +1,17 @@
+--- a/net/minecraft/server/BlockLectern.java
++++ b/net/minecraft/server/BlockLectern.java
+@@ -151,12 +151,13 @@
+     }
+ 
+     private void d(IBlockData iblockdata, World world, BlockPosition blockposition) {
+-        TileEntity tileentity = world.getTileEntity(blockposition);
++        TileEntity tileentity = world.getTileEntity(blockposition, false); // CraftBukkit - don't validate, type may be changed already
+ 
+         if (tileentity instanceof TileEntityLectern) {
+             TileEntityLectern tileentitylectern = (TileEntityLectern) tileentity;
+             EnumDirection enumdirection = (EnumDirection) iblockdata.get(BlockLectern.a);
+             ItemStack itemstack = tileentitylectern.getBook().cloneItemStack();
++            if (itemstack.isEmpty()) return; // CraftBukkit - SPIGOT-5500
+             float f = 0.25F * (float) enumdirection.getAdjacentX();
+             float f1 = 0.25F * (float) enumdirection.getAdjacentZ();
+             EntityItem entityitem = new EntityItem(world, (double) blockposition.getX() + 0.5D + (double) f, (double) (blockposition.getY() + 1), (double) blockposition.getZ() + 0.5D + (double) f1, itemstack);