Serial filter(...) expr: In some cases this breaks semantics

[maxkratz]

In some cases, serial filter(...) expressions break the filter semantics.
Example: Echtzeitsysteme/gips-tests#31

constraint -> global {
	mappings.n2n
	->filter(m | m.nodes().vnode.resourceDemand == 0)
	->filter(m | m.nodes().snode.resourceAmountTotal == 0)
	->count() == 0
}

Problem (if I understand it correctly):
If the first filter expression (in this case ->filter(m | m.nodes().vnode.resourceDemand == 0)) filters nothing out, i.e., the result should not be an empty set, the second filter(...) operation could not be triggered and, therefore, the count() does not evaluate to 0?