fixes https://github.com/spesmilo/electrum/issues/3315
The cause was that tracebacks look different whether stack items have source text available.
When using the pyinstaller windows binary, there is no source text available.
Example when running from source:
```
>>> a
Traceback (most recent call last):
File "...\electrum\gui\qt\console.py", line 256, in exec_command
result = eval(command, self.namespace, self.namespace)
File "<string>", line 1, in <module>
NameError: name 'a' is not defined
```
Example for pyinstaller windows binary:
```
>>> a
Traceback (most recent call last):
File "electrum\gui\qt\console.py", line 256, in exec_command
File "<string>", line 1, in <module>
NameError: name 'a' is not defined
```
ff53925811