Fails to update decay cursor when moving to new section.

[JoseGuzman]

To reproduce it:

1. Open the Cursor settings dialog (Edit->Cursor settings).
2. Open decay tab, click Start fit at the peak and press Apply.
3. Set peak cursors and the decay the second decay cursor, presss Enter.

The first decay cursor will be updated to the peak. After moving to a different sectionthe first decay cursor remains in the original position. It will not be updated to the peak cursor. :(

@JoseGuzman, check StfApp->SetFitStart() or StfApp->GetStartFitAtPeak()