SPIGOT-3107: Try and improve shield knockback further

nms-patches/EntityLiving.patch

@@ -529,7 +529,7 @@
 +
 +                return true;
 +            } else {
-+                return originalDamage > 0;
++                return (event.getDamage(DamageModifier.BLOCKING) < 0) ? false : originalDamage > 0;
 +                // CraftBukkit end
              }
          }