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.
diff --git a/layers/draw_state.cpp b/layers/draw_state.cpp
old mode 100644
new mode 100755
index 5bfe41d..8ab366f
--- a/layers/draw_state.cpp
+++ b/layers/draw_state.cpp
@@ -980,9 +980,11 @@
 static void deleteCmdBuffers()
 {
     for (unordered_map<VkCmdBuffer, GLOBAL_CB_NODE*>::iterator ii=cmdBufferMap.begin(); ii!=cmdBufferMap.end(); ++ii) {
-        while (!(*ii).second->pCmds.empty()) {
-            delete (*ii).second->pCmds.back();
-            (*ii).second->pCmds.pop_back();
+        vector<CMD_NODE*> cmd_node_list = (*ii).second->pCmds;
+        while (!cmd_node_list.empty()) {
+            CMD_NODE* cmd_node = cmd_node_list.back();
+            delete cmd_node;
+            cmd_node_list.pop_back();
         }
         delete (*ii).second;
     }