[ntuple] Merger: don't abort if a file doesn't contain a RNTuple

[silverweed]

The file without the RNTuple will simply be skipped. This mirrors the merge behavior of other ROOT objects.
Note that if the user gave the -ff or -fk options ("use first source compression") the compression will be taken from the first RNTuple found.

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    17 files      17 suites   4d 1h 26m 40s ⏱️
 2 690 tests  2 687 ✅ 0 💤 3 ❌
44 118 runs  44 115 ✅ 0 💤 3 ❌

For more details on these failures, see this check.

Results for commit 63b95b8.

♻️ This comment has been updated with latest results.

[hahnjo]

In principle LGTM, we probably want a test for this, in roottest? Also again a very picky comment (sorry): our own CONTRIBUTING.md says we should use present imperative mood, so the commit message should be "Merger: skip files without RNTuple".

[silverweed]

our own CONTRIBUTING.md says we should use present imperative mood, so the commit message should be "Merger: skip files without RNTuple".

But "don't abort" is present imperative; am I missing something?

[hahnjo]

But "don't abort" is present imperative

You are right. I thought we also prefer positive message instead negations (well, at least I do), but then please disregard.

[jblomer]

LGTM; please add a test, I'd suggest a unit test in ntuple_merger using TFileMerger.