Fixes #2903. Removing event hooks can AIOOB

Author: enebo

core/src/main/java/org/jruby/Ruby.java

@@ -3051,17 +3051,25 @@ public synchronized void addEventHook(EventHook hook) {
 
     public synchronized void removeEventHook(EventHook hook) {
         EventHook[] hooks = eventHooks;
+
         if (hooks.length == 0) return;
-        EventHook[] newHooks = new EventHook[hooks.length - 1];
-        boolean found = false;
-        for (int i = 0, j = 0; i < hooks.length; i++) {
-            if (!found && hooks[i] == hook && !found) { // exclude first found
-                found = true;
-                continue;
+
+        int pivot = -1;
+        for (int i = 0; i < hooks.length; i++) {
+            if (hooks[i] == hook) {
+                pivot = i;
+                break;
             }
-            newHooks[j] = hooks[i];
-            j++;
         }
+
+        if (pivot == -1) return; // No such hook found.
+
+        EventHook[] newHooks = new EventHook[hooks.length - 1];
+        // copy before and after pivot into the new array but don't bother
+        // to arraycopy if pivot is first/last element of the old list.
+        if (pivot != 0) System.arraycopy(hooks, 0, newHooks, 0, pivot);
+        if (pivot != hooks.length-1) System.arraycopy(hooks, pivot + 1, newHooks, pivot, hooks.length - (pivot + 1));
+
         eventHooks = newHooks;
         hasEventHooks = newHooks.length > 0;
     }