bug zero column projection does not persist row count across IPC

[coderfender]

Describe the bug

Utils.serializeBatches and Utils.coalesceBroadcastBatches lose the row
count when the input batch has zero columns, so a column-pruned broadcast
relation arrives at the receiver as empty.

Steps to reproduce

No response

Expected behavior

No response

Additional context

No response

[coderfender]

take