Set default CustomExplosion maxFallingBlocks to 0

This fixes an exception thrown when the trap rune in Wizards is
activated.

Plugins/Mineplex.Minecraft.Game.Core/src/mineplex/minecraft/game/core/explosion/CustomExplosion.java

@@ -53,7 +53,7 @@ public class CustomExplosion extends Explosion
 	private mineplex.core.explosion.Explosion _explosion;
 	private float _damage;
 	private boolean _useCustomDamage;
-	private int _maxFallingBlocks = -1;
+	private int _maxFallingBlocks = 0;
 	private float _maxDamage = 1000;
 	private float _size;
 	private boolean _damageBlocks = true;