Fix BTForEach crash if elements are removed from the array during iteration

(cherry picked from commit b8c9db0)

Author: limbonaut

bt/tasks/decorators/bt_for_each.cpp

@@ -43,12 +43,15 @@ void BTForEach::_enter() {
 }
 
 BT::Status BTForEach::_tick(double p_delta) {
-	ERR_FAIL_COND_V_MSG(get_child_count() == 0, FAILURE, "ForEach decorator has no child.");
-	ERR_FAIL_COND_V_MSG(save_var == StringName(), FAILURE, "ForEach save variable is not set.");
-	ERR_FAIL_COND_V_MSG(array_var == StringName(), FAILURE, "ForEach array variable is not set.");
+	ERR_FAIL_COND_V_MSG(get_child_count() == 0, FAILURE, "BTForEach: Decorator has no child.");
+	ERR_FAIL_COND_V_MSG(save_var == StringName(), FAILURE, "BTForEach: Save variable is not set.");
+	ERR_FAIL_COND_V_MSG(array_var == StringName(), FAILURE, "BTForEach: Array variable is not set.");
 
 	Array arr = get_blackboard()->get_var(array_var, Variant());
-	if (arr.size() == 0) {
+	if (current_idx >= arr.size()) {
+		if (current_idx != 0) {
+			WARN_PRINT("BTForEach: Array size changed during iteration.");
+		}
 		return SUCCESS;
 	}
 	Variant elem = arr[current_idx];

tests/test_for_each.h

@@ -96,6 +96,22 @@ TEST_CASE("[Modules][LimboAI] BTForEach") {
 		CHECK_ENTRIES_TICKS_EXITS(task, 3, 6, 3);
 		CHECK(blackboard->get_var("element", "wetgoop") == "mushroom");
 	}
+
+	SUBCASE("Shouldn't crash if elements are removed during iteration") {
+		CHECK(fe->execute(0.01666) == BTTask::RUNNING);
+		CHECK(task->get_status() == BTTask::SUCCESS);
+		CHECK_ENTRIES_TICKS_EXITS(task, 1, 1, 1);
+		CHECK(blackboard->get_var("element", "wetgoop") == "apple");
+
+		arr.clear();
+
+		ERR_PRINT_OFF;
+		CHECK(fe->execute(0.01666) == BTTask::SUCCESS); // Returns SUCCESS and prints a warning without executing child task.
+		ERR_PRINT_ON;
+		CHECK(task->get_status() == BTTask::SUCCESS); // Same status.
+		CHECK_ENTRIES_TICKS_EXITS(task, 1, 1, 1); // Task is not re-executed as there is not enough elements to continue iteration.
+		CHECK(blackboard->get_var("element", "wetgoop") == "apple"); // Not changed.
+	}
 }
 
 } //namespace TestForEach