Fix bug in scaling intensity combination affecting multisweep datasets.

[jbeilstenedmands]

Affects the Imid midpoint value scoring in the intensity combination for multi sweep datasets only (doesn't affect the scoring of prf and sum).
Issue was repeated multiplication by the correction that was being accumulated in the loop over Imid values.

Fixes #1927

Thanks for @huwjenkins for investigative work here and confirming the fix.

[codecov]

Codecov Report

Merging #2199 (0ed2d27) into main (1096557) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 0ed2d27 differs from pull request most recent head fe89aed. Consider uploading reports for the commit fe89aed to get more accurate results

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