Previously, 'read-error' exceptions other than "missing closing paren"
would not be reported; instead, we'd directly call (exit 1) without
printing anything.
Fixes <https://issues.guix.gnu.org/51463>.
Reported by Alice BRENON <alice.brenon@ens-lyon.fr>.
* guix/ui.scm (report-load-error): Report the error without re-throwing
upon 'read-error'.
* tests/guix-build.sh: Add test.