Redundant call to decodeError in DebugUserOpController - When let errorObject from params is null/undefined

## Description
If the `errorObject` is null or undefined, then no need to call the code block which does `decodeError`
In such case `decodedErrors` in response can stay null

## Code Loc:
[DebugUserOpController => decodeError](https://github.com/bcnmy/userop-debugger-backend/blob/main/src/controller/DebugUserOpController.ts#L29-L42)

```ts
if(errorObject) {
try {
let errorDecoderService = getErrorDecoderService(networkId);
if (errorDecoderService) {
decodedErrors = await errorDecoderService.decodeError({
networkId,
entryPointAddress,
error: errorObject,
userOp: userOperation
});
}
} catch (error) {
console.error("Error decoding error object: ", error);
// Handle or log the error as appropriate
}
}
```

Read src/controller/DebugUserOpController.ts at lines 29-42 and trace how errorObject and decodedErrors are handled when the input is null or undefined. Confirm that decoding is skipped in that case, decodedErrors remains null, and the existing error-decoding behavior is unchanged when an error object is present.

Written by the indexing model from the issue text.