types: Fix warning for multiple map occurrences

AddMapEntry may emit a warning even if told to not report. This is problematic when it is called by CopyDefToKeyType, as AddMapEntry is used there for adding default map entries corresponding to each preserve entry, only if relevant. These default entries should not trigger a warning (report = False) if conflicting with an existing entry and simply be ignored. However with the current code a warning may be erroneously emitted if one set the warning level >=9, leaving the user puzzled with a conflicting map entry found nowhere in the source files.