SPIGOT-5951: Projectile#getShooter() returns null

By: md_5 <git@md-5.net>

paper-server/nms-patches/IProjectile.patch

@@ -15,7 +15,7 @@
              this.shooter = entity.getUniqueID();
              this.c = entity.getId();
          }
-+        this.projectileSource = (entity instanceof ProjectileSource) ? (ProjectileSource) entity.getBukkitEntity() : null; // CraftBukkit
++        this.projectileSource = (entity != null && entity.getBukkitEntity() instanceof ProjectileSource) ? (ProjectileSource) entity.getBukkitEntity() : null; // CraftBukkit
  
      }