Evaluating a C++ new expression now includes generating an intermediate
ExplodedNode, and this node could very well represent a previously-
reachable state in the ExplodedGraph. If so, we can short-circuit the
rest of the evaluation.

Caught by the assertion a few lines later.

<rdar://problem/13510065>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178401 91177308-0d34-0410-b5e6-96231b3b80d8