[mc] Fix lookup of malloc fragment type

[mc] Fix lookup of malloc fragment type

In some cases, the type was looked up in the current heapinfo and not
in the snapshot one:

 * in some cases this is not an issue as state->heapinfo2 is currently
   the same as the current heapinfo but this solution is more robust;

 * if we were supposed to look it from state->heapinfo1 this is wrong.