AST-1638 Fix flag counting in UVWFlagger when using BDA

UVWFlagger did not count flags since pointers were equal. Also prepare UVWFlagger for BdaBuffer rows without pointers.

requested review from @dijkema

assigned to @mnijhuis-tos

added 4 commits

• 418578c7...ad3a70cc - 2 commits from branch master
• be2b1a44 - Fix flag counting in UVWFlagger when using BDA
• bb10c68b - Rename 'j' to 'channel'

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approved this merge request

merged

mentioned in commit 48e75b34