Prallel task execution error on Postgres backend

[mrjmarcelo]

If you try to execute tasks in parallel in Postgres backend, you will get the error below:

(orchestration-processor: failed to complete work item: failed to insert into the NewTasks table: ERROR: could not determine data type of parameter $3 (SQLSTATE 42P18))

To reproduce the issue just set a Postgres backend to parallel sample, the error happens when we have trigged two or more activities by CallActivity method, then you call Await. When you call Await, the system will lock the execution and throw this error infinitely.

[mrjmarcelo]

The issue is in the line 314 of "backend\postgres\postgres.go" source file. The SQL statatement has two parameters (InstanceID, EventPayload), but the when the offset factor used in string builder is incorrectly set to 3 instead of 2:

Set the offset factor to 2 in this case, and the parallel execution will work fine for PostgreSQL database.