SPIGOT-6125: Grass path should only fade when it is invalid at that location

nms-patches/BlockGrassPath.patch

@@ -0,0 +1,14 @@
+--- a/net/minecraft/server/BlockGrassPath.java
++++ b/net/minecraft/server/BlockGrassPath.java
+@@ -31,6 +31,11 @@
+ 
+     @Override
+     public void tickAlways(IBlockData iblockdata, WorldServer worldserver, BlockPosition blockposition, Random random) {
++        // CraftBukkit start - do not fade if the block is valid here
++        if (iblockdata.canPlace(worldserver, blockposition)) {
++            return;
++        }
++        // CraftBukkit end
+         BlockSoil.fade(iblockdata, worldserver, blockposition);
+     }
+