Fix: continueOnFail error management

I observed some weird behaviors when testing a custom node which was used with `continueOnFail()`, and would return the items, as is done in this example.

## Issues:

- Records are being pushed in the `items` array within a loop over them, this essentially causes an infinite loop. I fixed that loop by adding `itemCount` 
- Upon fixing the infinite loop, I noticed both `success` and `error` branches of the node would activate, that was because the pushed item had an `error` field (which triggers the error branch), but the original item was still present without an error field (which trigger the success branch)

There may be better fixes to this, but this approach worked for me.

nodes/ExampleNode/ExampleNode.node.ts

@@ -39,6 +39,7 @@ export class ExampleNode implements INodeType {
 	// You can make async calls and use `await`.
 	async execute(this: IExecuteFunctions): Promise<INodeExecutionData[][]> {
 		const items = this.getInputData();
+		const itemCount = items.length;
 
 		let item: INodeExecutionData;
 		let myString: string;
@@ -46,7 +47,7 @@ export class ExampleNode implements INodeType {
 		// Iterates over all input items and add the key "myString" with the
 		// value the parameter "myString" resolves to.
 		// (This could be a different value for each item in case it contains an expression)
-		for (let itemIndex = 0; itemIndex < items.length; itemIndex++) {
+		for (let itemIndex = 0; itemIndex < itemCount; itemIndex++) {
 			try {
 				myString = this.getNodeParameter('myString', itemIndex, '') as string;
 				item = items[itemIndex];
@@ -56,7 +57,7 @@ export class ExampleNode implements INodeType {
 				// This node should never fail but we want to showcase how
 				// to handle errors.
 				if (this.continueOnFail()) {
-					items.push({ json: this.getInputData(itemIndex)[0].json, error, pairedItem: itemIndex });
+					items[itemIndex].error = error;
 				} else {
 					// Adding `itemIndex` allows other workflows to handle this error
 					if (error.context) {