Statistics in Final VI batch not updated

[waelbenamara]

Describe the bug

When using LDA with --minibatch > 1, the final partial batch is processed for learning but not counted in the reported statistics, causing an incorrect "number of examples" count.
Root Cause:
The update_stats_lda() function only updates statistics when batch_buffer.size() == minibatch, excluding the final partial batch

How to reproduce

./vw --lda 20 -d dataset.vw --minibatch 256 --passes 1

Version

9.10.0

OS

linux

Language

C++

Additional context

I have a fix ready should I PR?