Slogger has off-by-one in slogging of deliveryNum

[FUDCo]

Describe the bug

An incidental discover in the examination of #3021 is that the slogger increments deliveryNum before it is done outputting all the slog entries generated in the processing of a delivery, the result of which is that while the entry for the delivery itself as well as the delivery result at the end shows the correct delivery number, all the slog entries framed by these show a delivery number one greater.

This is disambiguated by context when all slog entries are read in chronological order, but if a filter was applied just to extract selected entries, this context might not be present.

To Reproduce

Turn on slogging, send some messages that produce activity, examine the deliveryNum field in slog entries that contain one.

Expected behavior

The deliveryNum value in slog entries should match the delivery number of the delivery they are describing.

[FUDCo]

Closed by #3059