Description of work

This PR fixes a bug where the Full FunctionBrowser and Template FunctionBrowser on the QENS Fitting interface could go out of sync when all functions are removed from either one, before switching to a different view.

Fixes #37199

To test:

Open Inelastic->QENS Fitting
Go to IqtFit tab
Select Stretched Exp as Fit type
Tick See full function, it should have the stretched exp
Untick See full function
Select None as Fit type
Tick See full function, it should be empty.

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