Minor Fixes in the Emacs extension

[Alidra]

This PR fixes some minor issues in the Emacs extension (package). Specifically :

• The Goals panel is recentred to show the first goal in case of many assumptions and avoid having to scroll down.
• When proofs are navigated, if the last command is reached, the navigation continues to the end of file to display the last error messages if any (in particular the issue described in In Emacs, the syntax error message at the end of a file, is not displayed in the console #1111 where the end; token is missing)

[Alidra]

Please note that in case no next command exists but some empty lines, theses empty lines are highlighted to the end of file. I dont know if this is ok?