Hotfixes for XPS reader

[lukaspie]

• Fixes issue with channel reading
• Linking with multiple entries partially resolved (see also [Bug]: Handling of links pynxtools-xps#2)

[coveralls]

Pull Request Test Coverage Report for Build 7633239648

• 12 of 15 (80.0%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.005%) to 44.579%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pynxtools/dataconverter/readers/xps/reader.py	12	13	92.31%
pynxtools/dataconverter/readers/xps/sle/sle_specs.py	0	1	0.0%
pynxtools/dataconverter/readers/xps/txt/txt_scienta.py	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
pynxtools/nexus/nxdl_utils.py	2	74.95%

Totals
Change from base Build 7632295519:	-0.005%
Covered Lines:	4905
Relevant Lines:	11003

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💛 - Coveralls

[lukaspie]

Hey @domna, can we merge these changes? They are needed for the north example to work.

[domna]

LGTM. Sorry, I did not review because this was still set as a draft.

[lukaspie]

Right, my bad. Thanks for the review.