Fix xcmp message processing condition.

[shaunxw]

The messages processing loop shouldn't be entered again if there is no message left. Before this fix, calling handle_xcmp_messages with one message would panic.

cumulus/pallets/xcmp-queue/src/lib.rs

Line 609 in 1bb5e2a

fn handle_xcmp_messages<'a, I: Iterator<Item = (ParaId, RelayBlockNumber, &'a [u8])>>(

cumulus/pallets/xcmp-queue/src/lib.rs

Lines 522 to 528 in 1bb5e2a

	let weight_processed = if status[index].2.is_empty() {
	debug_assert!(
	false,
	"channel exists in status; there must be messages; qed"
	);
	0
	} else {

Fixes: #473

[apopiak]

add a smoke test?

[bkchr]

add a smoke test?

#400

@apopiak can you review this?

[gavofyork]

A test would be nice.

[apopiak]

add a smoke test?

#400

@apopiak can you review this?

@bkchr Do you mean that it's fine to merge as-is without a test because we have a tracking issue?

[shawntabrizi]

@apopiak no we should add a test here. If you can, add one, if not, I will do it later today

[shawntabrizi]

@apopiak please take a look and merge if you think it is okay