open save dialog either in the user save directory or the last used
for saving files from the instruemnt view. Re #6130.

last commit introduced a bug instead of correcting. Now, only
exceptions related to no detector associated is ignored.

re #6061

(They were somehow 'lost' from a previous commit)

re #6061

If you don't load everything the resulting crop gives the wrong spectra
since it goes by index not spectrum and assumes an off-by-one value.

Refs #6757

re #6759