Load algorithm dialog with LoadSQW does not treat OutputFilename correctly

[Martyn Gigg]

Discovered while testing #9862.

To reproduce use the sqw described in the above ticket:

• Click Load and browse to the SQW file
• At the bottom of the dialog click browse for the OutputFilename argument and select a file.
• The dialog will state that the property has an error that the file cannot be found despite it being a file that is not supposed to exist yet.
• Clicking run just ignores the property error and the algorithm proceeds just as if the property was left blank.

The same behaviour does not happen if you run LoadSQW so the problem is specific to Load dialog.

[Nick Draper]

Moved to the backlog at the code freeze of R3.3

[Stuart Campbell]

This ticket has been transferred to github issue ​11204