Crash when trying to fit a tie on QENS Fitting interface.

[adriazalvarez]

This crash is produced when trying to fit a tie to itself. An error message appears, but Mantid also crashes.

Original reporter: Mona Sarter

Describe the bug

To Reproduce

• Go to Interfaces -> Inelastic -> QENS Fitting -> I(Q,t) Fit tab
• Add Workspace button and add from file irs26176_graphite002_iqt.nxs
• On Fit Function Browser, select Fit Type and click on Stretch Exponential
• Three parameters should appear below. Select Lifetime and click on the parameter edit (a button with three dots ... should appear, click it an open the Edit Parameter Values dialog.
• On the dialog, select the first spectra and click on Set button, and then Set Tie from the drop-down.
• On the tie edit, write: Lifetime and click Ok, and then Ok again on the Edit Parameter Dialog.
• Mantid will crash.

Expected behavior
Only the error message should appear, with no crash.

Screenshots

Platform/Version (please complete the following information):

• OS: Windows
• OS Version: 10
• Mantid Version 6.9.1 and Nightly

Additional context