lead fix and unloaded entity fix

src/main/java/carpet/mixins/MobEntity_leashMixin.java

@@ -0,0 +1,28 @@
+package carpet.mixins;
+
+import carpet.settings.CarpetSettings;
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.mob.MobEntity;
+import net.minecraft.nbt.CompoundTag;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(MobEntity.class)
+public abstract class MobEntity_leashMixin
+{
+    @Shadow /*@Nullable*/ private Entity holdingEntity;
+
+    @Shadow /*@Nullable*/ private CompoundTag leashTag;
+
+    @Inject(method = "writeCustomDataToTag", at = @At("TAIL"))
+    private void addLeashData(CompoundTag compoundTag_1, CallbackInfo ci)
+    {
+        if (holdingEntity == null && CarpetSettings.leadFix && leashTag != null)
+        {
+            compoundTag_1.put("Leash", leashTag);
+        }
+    }
+}