Avoid 0 rewards conversions in MASP transactions #4789
Description
When building MASP txs we convert the assets of the user to their latest available counterpart. There's a chance though, that the applied conversion doesn't bring in any rewards but just converts the asset to the latest masp epoch (this could happen if no rewards had been produced for that specific asset).
In this case, the builder will include the conversion but this is technically useless, as it brings nothing to the involved amounts and only takes up resources, namely space in the transaction (which might also turn into possible issues with the hardware wallet) and gas to verify these conversions (both to verify their anchors and for the convert circuit).
We could try to modify apply_conversion to remove such conversion from Conversions if that's the case
cc: @mateuszjasiuk