Fix ability to delete warps in unloaded worlds (EssentialsX#4590)

Fixes EssentialsX#4584.

Author: JRoy

Essentials/src/main/java/com/earth2me/essentials/Warps.java

@@ -38,6 +38,11 @@ public boolean isEmpty() {
         return warpPoints.isEmpty();
     }
 
+    @Override
+    public boolean isWarp(String name) {
+        return warpPoints.containsKey(new StringIgnoreCase(name));
+    }
+
     @Override
     public Collection<String> getList() {
         final List<String> keys = new ArrayList<>();

Essentials/src/main/java/com/earth2me/essentials/api/IWarps.java

@@ -26,6 +26,14 @@ public interface IWarps extends IConf {
      */
     Location getWarp(String warp) throws WarpNotFoundException, net.ess3.api.InvalidWorldException;
 
+    /**
+     * Checks if the provided name is a warp.
+     *
+     * @param name The warp name.
+     * @return true if a warp by that name exists.
+     */
+    boolean isWarp(String name);
+
     /**
      * Gets a list of warps
      *

Essentials/src/main/java/com/earth2me/essentials/commands/Commanddelwarp.java

@@ -23,8 +23,14 @@ public void run(final Server server, final CommandSource sender, final String co
             throw new NotEnoughArgumentsException();
         }
         //Check if warp exists before calling the event
-        final Location location = ess.getWarps().getWarp(args[0]);
-        if (location != null) {
+        if (ess.getWarps().isWarp(args[0])) {
+            Location location;
+            try {
+                location = ess.getWarps().getWarp(args[0]);
+            } catch (Exception ignored) {
+                // World is unloaded/deleted
+                location = null;
+            }
             final WarpModifyEvent event = new WarpModifyEvent(sender.getUser(this.ess), args[0], location, null, WarpModifyEvent.WarpModifyCause.DELETE);
             Bukkit.getServer().getPluginManager().callEvent(event);
             if (event.isCancelled()) {

Essentials/src/main/java/net/essentialsx/api/v2/events/WarpModifyEvent.java

@@ -23,7 +23,7 @@ public class WarpModifyEvent extends Event implements Cancellable {
     /**
      * @param user        the {@link IUser} who is modifing the warp.
      * @param warpName    the name of the warp that's being altered.
-     * @param oldLocation the old location before being modified. Null if {@link WarpModifyCause#CREATE}.
+     * @param oldLocation the old location before being modified. Null if {@link WarpModifyCause#CREATE} or if the previous location's world is not loaded.
      * @param newLocation the new location after being modified. Null if {@link WarpModifyCause#DELETE}.
      * @param cause       the cause of change.
      */
@@ -58,7 +58,7 @@ public String getWarpName() {
     }
 
     /**
-     * Gets the current location of the warp or null if it's being created.
+     * Gets the current location of the warp or null if it's being created or if the previous location's world is not loaded.
      * @return The warps new location or null.
      */
     public Location getOldLocation() {