Preserve initial velocity of spawned entities - Fixes #4292

Spigot-Server-Patches/0575-Fix-Entity-Teleportation-and-cancel-velocity-if-tele.patch

@@ -9,14 +9,28 @@ as this is how Vanilla teleports entities.
 Cancel any pending motion when teleported.
 
 diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
-index 3e6ccdd5b54dbe51d4ee9ec979cbc2d0f335be70..abdc68fce1ebb70ab6a25188ec1773ccbb8f37a6 100644
+index 3e6ccdd5b54dbe51d4ee9ec979cbc2d0f335be70..5e1978d1c96dede07ead967c1e85a352348e7777 100644
 --- a/src/main/java/net/minecraft/server/Entity.java
 +++ b/src/main/java/net/minecraft/server/Entity.java
-@@ -1316,6 +1316,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
+@@ -54,6 +54,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
+ 
+     // CraftBukkit start
+     private static final int CURRENT_LEVEL = 2;
++    boolean preserveMotion = true; // Paper - keep initial motion on first setPositionRotation
+     static boolean isLevelAtLeast(NBTTagCompound tag, int level) {
+         return tag.hasKey("Bukkit.updateLevel") && tag.getInt("Bukkit.updateLevel") >= level;
+     }
+@@ -1316,6 +1317,13 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
      }
  
      public void setPositionRotation(double d0, double d1, double d2, float f, float f1) {
-+        this.mot = new Vec3D(0, 0, 0); // Paper - cancel entity velocity if teleported
++        // Paper - cancel entity velocity if teleported
++        if (!preserveMotion) {
++            this.mot = Vec3D.ORIGIN;
++        } else {
++            this.preserveMotion = false;
++        }
++        // Paper end
          this.g(d0, d1, d2);
          this.yaw = f;
          this.pitch = f1;