Need better feedback to user when fitting fails to converge

[butler]

As of version 4.1, when the fitting fails to converge or hits a singularity etc, there are two responses. For sum/multiply (including P*S) models which are still in the old SasView infrastructure a pop up with the traceback … which is extremely confusing to the user and not helpful. For regular models that use the sasmodels infrastructure, a message is sent to the console stating that no values were returned from the fitter and a warning that fitting did not converge. Also the corner of the console line goes red. However the console line stays blank.

The first issue will get resolved when the sum/multiply get moved to the product model in the sasmodels infrastructure.

Two other things are being requested in order to make this useful:

• Send the message also to a popup
• To the "fitting did not converge" add some suggestions for what might help such as "you might want to check your starting parameters"

[richardh]

See also #866 which give specific example of NaN values returned from Hayter_MSA