No errors/feedback for save errors

[lspector]

Saving to an invalid path, and maybe other errors currently fail silently.

[MawiraIke]

Hello @benfb . Thanks for maintaining the awesome library, I totally enjoy using it. I got some time in my hands and would like to contribute to the library and work on some fixes. This issue seems like a good starting point for me, 1) are you still open to a PR concerning the same?
2) I can see that the current code throws a common alert for every error, i.e Failed to save worksheet. Did you intend to show different errors according to the error thrown e.g File not found etc.

Again, thanks for the library.
Regards,
Ike.