crash in attribute after tango DS restart (when events are blocked)
Didn't have time to investigate, but here is how to reproduce it (100% of the times in my case, with pytango 9.3.1, tango 9.3.2):
1. Start tangotest DS
2. launch this client:
```python
from taurus.qt.qtgui.application import TaurusApplication
from taurus.qt.qtgui.input import TaurusValueLineEdit
import sys
app = TaurusApplication(cmd_line_parser=None)
w = TaurusValueLineEdit()
w.setModel("sys/tg_test/1/short_scalar")
w.show()
sys.exit(app.exec_())
```
3. stop the tangotest DS (the line edit receives an error event and gets disabled, as expected)
4. start the tangotest DS (the line edit receives a valid event and gets enabled, as expected)
5. wait a few seconds (~10?) and the line edit crashes
Maybe this is related to #tango-controls/cppTango#686 ?
issue