msxml3: Initialise output interface pointers to NULL in xmlnodelist_QueryInterface and xmlnodelist_nextNode.

This is needed because IRpcStubBuffer::Invoke should not allow RPC
exceptions to be passed to the caller.

ComplexStructMemorySize from NdrComplexArrayUnmarshall.

to validate the conformance values being read from the wire.

exception if a multiply overflows a 4-byte integer.

This will protect the unmarshaling code against attacks specifying a 
large variance.
Use this new function in the conformant string functions to harden them 
against attack.