[Feature Request]: Text file input - add a log warning/error if no file is selected/found

### What would you like to happen?

The **Text file input** transform gives no evidence in the (Basic) log if none of the selected input files is found: you get only the opposite evidence, i.e. the list of files that are being opened.

Moreover, in this case the transform proceeds as it was dealing with an empty stream, causing not-so-expected results sometimes: e.g. if used as lookup for a Stream lookup transform, the main stream traverses the transform without any lookup info attached (would be fine if the lookup file was actually empty, not so fine if it doesn't exist)

### Issue Priority

Priority: 2

### Issue Component

Component: Transforms

Start by locating the Text file input transform and its Basic log handling, then review how it reports files being opened. Check the interaction with Stream lookup when no input file is found; done means the log clearly reports the missing selection or file and the transform no longer silently behaves like an empty stream.

Written by the indexing model from the issue text.