Refactor tpaccept world permission checks for clarity

When mdcfe in `world_nether` sends a `/tpa` to mdcfe3 in `world` and mdcfe3 accepts:
```
[13:57:02 INFO]: mdcfe3 issued server command: /tpaccept
[...]
[13:57:02 INFO]: [Essentials] checking if mdcfe3 has essentials.tpaccept - true
[...]
[13:57:02 INFO]: [Essentials] checking if mdcfe has essentials.tpa - true
[13:57:02 INFO]: [Essentials] checking if mdcfe has essentials.worlds.world - true
```

When mdcfe in `world` sends a `/tpahere` to mdcfe3 in `world_nether` and mdcfe3 accepts:
```
[14:02:36 INFO]: mdcfe3 issued server command: /tpaccept
[...]
[14:02:36 INFO]: [Essentials] checking if mdcfe3 has essentials.tpaccept - true
[...]
[14:02:36 INFO]: [Essentials] checking if mdcfe has essentials.tpahere - true
[14:02:36 INFO]: [Essentials] checking if mdcfe3 has essentials.worlds.world - true
```

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

@@ -8,6 +8,7 @@ import net.essentialsx.api.v2.events.TeleportRequestResponseEvent;
 import org.bukkit.Bukkit;
 import org.bukkit.Location;
 import org.bukkit.Server;
+import org.bukkit.World;
 import org.bukkit.event.player.PlayerTeleportEvent.TeleportCause;
 
 import java.util.ArrayList;
@@ -87,12 +88,15 @@ public class Commandtpaccept extends EssentialsCommand {
             throw new Exception(tl("noPendingRequest"));
         }
 
-        if (request.isHere() && ((!requester.isAuthorized("essentials.tpahere") && !requester.isAuthorized("essentials.tpaall")) || (user.getWorld() != requester.getWorld() && ess.getSettings().isWorldTeleportPermissions() && !user.isAuthorized("essentials.worlds." + user.getWorld().getName())))) {
-            throw new Exception(tl("noPendingRequest"));
-        }
-
-        if (!request.isHere() && (!requester.isAuthorized("essentials.tpa") || (user.getWorld() != requester.getWorld() && ess.getSettings().isWorldTeleportPermissions() && !user.isAuthorized("essentials.worlds." + requester.getWorld().getName())))) {
-            throw new Exception(tl("noPendingRequest"));
+        if (request.isHere()) {
+            final boolean isRequesterAuthorized = requester.isAuthorized("essentials.tpahere") || requester.isAuthorized("essentials.tpaall");
+            if (!isRequesterAuthorized || !canTeleportToWorld(user, requester.getWorld())) {
+                throw new Exception(tl("noPendingRequest"));
+            }
+        } else {
+            if (!requester.isAuthorized("essentials.tpa") || !canTeleportToWorld(requester, user.getWorld())) {
+                throw new Exception(tl("noPendingRequest"));
+            }
         }
 
         final TeleportRequestResponseEvent event = new TeleportRequestResponseEvent(user, requester, request, true);
@@ -129,4 +133,8 @@ public class Commandtpaccept extends EssentialsCommand {
         }
         user.removeTpaRequest(request.getName());
     }
+
+    private boolean canTeleportToWorld(final User user, final World destination) {
+        return user.getWorld() == destination || !ess.getSettings().isWorldTeleportPermissions() || user.isAuthorized("essentials.worlds." + destination.getName());
+    }
 }