Histogram merging: Fix HLT use-case

While testing !78484 (merged), I overlooked one use-case that surfaced now as ADCSUPPORT-5725.

With this MR, the DQHistogramMerge job can deal with input files that contain no "run_NNNNN" directory at top level and that contain no metadata trees in the indiviual sub-directories.

Closes ADCSUPPORT-5725

added bugfix label

This merge request affects 1 package:

• DataQuality/DataQualityUtils

This merge request affects 1 file:

• DataQuality/DataQualityUtils/src/MonitoringFile.cxx

added 24.0 DQ review-pending-level-1 labels

CI Result SUCCESS (hash eb9f29a6)

	Athena
externals
cmake
make
tests

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Changes are fine and CI succeeds, approving for L1. -L1

added review-approved label and removed review-pending-level-1 label

added review-approved-tier0 label

mentioned in commit 2623015b

merged

mentioned in merge request !78769 (merged)