Fix #3725: DbBatchBatcher empty batch execution bug

[ja-kar]

Fixes #3725

Description

DbBatchBatcher throws InvalidOperationException when attempting to execute an empty batch, while
GenericBatchingBatcher and SqlClientBatchingBatcher handle this scenario correctly.

Root Cause

DbBatchBatcher.DoExecuteBatch() and DoExecuteBatchAsync() lack empty batch validation. When ExecuteBatch()
is called with an empty batch (_currentBatch.BatchCommands.Count == 0), the code attempts to execute a DbBatch
with no commands, causing:

System.InvalidOperationException: ExecuteNonQuery: CommandText property has not been initialized

Changes

Added empty batch check at the beginning of both methods, matching the pattern used in GenericBatchingBatcher:

if (_currentBatch.BatchCommands.Count == 0)
{
    Expectations.VerifyOutcomeBatched(_totalExpectedRowsAffected, 0, ps);
    return;
}

Modified:

• src/NHibernate/AdoNet/DbBatchBatcher.cs - Added guard clauses to DoExecuteBatch() and DoExecuteBatchAsync()

Added:

• Test cases in src/NHibernate.Test/Ado/BatcherFixture.cs verifying the fix
• Generated async test counterparts

[gliljas]

Good catch and thanks for the fix!

My very personal reflection is that your tests should be included in the normal batcher tests, rather than as a NHSpecificTest.

[ja-kar]

Good point! I'll move the tests