crypt32: When removing contexts from a list, make sure the context no longer references the list.

dlls/crypt32/context.c

@@ -289,6 +289,7 @@ void ContextList_Delete(struct ContextList *list, void *context)
     EnterCriticalSection(&list->cs);
     list_remove(entry);
     LeaveCriticalSection(&list->cs);
+    list_init(entry);
     list->contextInterface->free(context);
 }