draw_state: Fix Microsoft C++ iterator assert
draw_state: Fix Microsoft C++ iterator assert

The Microsoft Visual Studio vector library does not like this code:
delete (*ii).second->pCmds.back();

Internally, pCmds.back() does a pCmds.end() - 1 and since the
vector we are using (*ii).second->pCmds is not local, the library
throws an assert about the iterator being non-incrementable.
The assert if fixed by making a local copy of the vector and
working on that.

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools