The stream may have read some data already (such as the stream
header). When initially writing this code, I had missed that we do
actually also carry the parser state over: I misread the
AsyncReader::wrap(..) command as something like AsyncReader::new, i.e.
starting off with fresh parser state, so I assumed that we need a fresh
XmlLangStack, too.
This is wrong: `p` comes from `self.parser.into_inner()` above and is
the parser state, so we need to carry the lang stack along, as well.
This fixes:
```
thread 'tokio-runtime-worker' panicked at […]/rxml-0.13.1/src/xml_lang.rs:87:13:
pop from empty XmlLangStack
```
happening during stream shutdown. The panic was first reported by
@ppjet6, so thanks for that and the keen eye.
skip-changelog, because the bug has not been released yet.
51ce661f8d
