SPIGOT-6311: Don't calculate portal shapes for up/down directions

nms-patches/BlockFireAbstract.patch

@@ -33,7 +33,20 @@
      }
  
      @Override
-@@ -103,4 +110,12 @@
+@@ -83,6 +90,12 @@
+     }
+ 
+     private static boolean b(World world, BlockPosition blockposition, EnumDirection enumdirection) {
++        // CraftBukkit start - SPIGOT-6311: Do not calculate portals for up/down directions
++        if (enumdirection == EnumDirection.UP || enumdirection == EnumDirection.DOWN) {
++            return false;
++        }
++        // CraftBukkit end
++
+         if (!a(world)) {
+             return false;
+         } else {
+@@ -103,4 +116,12 @@
              return flag && BlockPortalShape.a((GeneratorAccess) world, blockposition, enumdirection.h().n()).isPresent();
          }
      }