Fix ActionLog BAO to not overwrite existing data

[colemanw]

Overview

I spotted what looks like a bug in this BAO code. create functions in the BAO serve a double-duty, they are also used for update. So when setting defaults, one must be careful to check which operation is happening before possibly overwriting existing data.

Before

Default set unconditionally, existing data overwritten.

After

Default only set for create action.

[civibot]

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