[zypp] Fix possible memory leaks with heap-allocated items vector

In some cases (exception handling / early return), delete might not
be called on the items vector. As there's no need for the vector to
be alive for longer than the function duration, just make it a local
variable on the stack.
Merge pull request #37 from thp/stack-allocation

[zypp] Fix possible memory leaks with heap-allocated items vector