x/claimsmanager/keeper: clarify why .Claims filterPaginate ends iteration on finding a single claim with the same chainId

[odeke-em]

I was just auditing the code in here and wondered why this condition exists

quicksilver/x/claimsmanager/keeper/grpc_query.go

Lines 35 to 38 in 7966553

	if claim.ChainId == req.ChainId {
	claims = append(claims, claim)
	return true, nil
	}

Is that there will be exactly one claim per chainID and if so, can we please add a comment in that code about the invariant/assumption? Thank you

/cc @joe-bowman @faddat