HPCC-31652 Guard against calculateSkew causing attach to fail

[jakesmith]

When attaching a file to DFS it performs a skew calculation, which may check physical file parts if there are missing size attributes. If a physical file is missing during this process, it will cause attach() to fail.
A pull Roxie attaches a logical file without the physical files being present, if size attributes are missing it will fail. Protect against this failure in the skew calculation (catch exception, log and continue).

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[github-actions]

Jira Issue: https://hpccsystems.atlassian.net//browse/HPCC-31652

Jirabot Action Result:
Workflow Transition: Merge Pending
Updated PR

[mckellyln]

Minor, I might also set:
minSkew = maxSkew = 0;
here so they are set if an exception occurred, but I don't think these args are ever used if this routine returns false so it doesn't really matter.

[mckellyln]

Approved