Fix Linear pattern index incrementing above array length (#2626)

* Fix index incrementing above array length in async

* Add fork method

worldedit-core/src/main/java/com/fastasyncworldedit/core/function/pattern/LinearBlockPattern.java

@@ -1,5 +1,6 @@
 package com.fastasyncworldedit.core.function.pattern;
 
+import com.fastasyncworldedit.core.queue.Filter;
 import com.sk89q.worldedit.WorldEditException;
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.pattern.AbstractPattern;
@@ -7,6 +8,8 @@ import com.sk89q.worldedit.function.pattern.Pattern;
 import com.sk89q.worldedit.math.BlockVector3;
 import com.sk89q.worldedit.world.block.BaseBlock;
 
+import java.util.Arrays;
+
 public class LinearBlockPattern extends AbstractPattern implements ResettablePattern {
 
     private final Pattern[] patternsArray;
@@ -15,7 +18,7 @@ public class LinearBlockPattern extends AbstractPattern implements ResettablePat
     /**
      * Create a new {@link Pattern} instance
      *
-     * @param patterns array of patterns to linearly choose from based on x/z coordinates
+     * @param patterns array of patterns to linearly choose from
      */
     public LinearBlockPattern(Pattern[] patterns) {
         this.patternsArray = patterns;
@@ -23,18 +26,20 @@ public class LinearBlockPattern extends AbstractPattern implements ResettablePat
 
     @Override
     public BaseBlock applyBlock(BlockVector3 position) {
-        if (index == patternsArray.length) {
-            index = 0;
-        }
-        return patternsArray[index++].applyBlock(position);
+        index = (index + 1) % patternsArray.length;
+        return patternsArray[index].applyBlock(position);
     }
 
     @Override
     public boolean apply(Extent extent, BlockVector3 get, BlockVector3 set) throws WorldEditException {
-        if (index == patternsArray.length) {
-            index = 0;
-        }
-        return patternsArray[index++].apply(extent, get, set);
+        index = (index + 1) % patternsArray.length;
+        return patternsArray[index].apply(extent, get, set);
+    }
+
+    @Override
+    public Filter fork() {
+        final Pattern[] forked = Arrays.stream(this.patternsArray).map(Pattern::fork).toArray(Pattern[]::new);
+        return new LinearBlockPattern(forked);
     }
 
     @Override