[Bug]: Data Grid + Metadata Injection - single columns are not injected without separator

### Apache Hop version?

2.11, 2.12

### Java version?

17.0.2

### Operating system

Linux

### What happened?

Injection of a single column in a Data grid transform is not correct when a separator is not specified: the single columns is created, but all the values are empty/nulls.

Check discussion #5128 for an example use case and possible workarounds.

**_Issue is not present on version 2.10_**

### Issue Priority

Priority: 2

### Issue Component

Component: Metadata, Component: Transforms

Start with the Data grid transform's metadata injection path and compare behavior between versions 2.10 and 2.11/2.12, using discussion #5128 for the example and workarounds. Reproduce a single-column injection without a separator; done means the column is populated with its input values rather than empty or null values.

Written by the indexing model from the issue text.