Prior to this change, errors such as wrong permissions on
/etc/guix/signing-key.sec would give:
guix-daemon: nix/libutil/serialise.cc:15: virtual nix::BufferedSink::~BufferedSink(): Assertion `!bufPos' failed.
This patch correctly propagates the error to the client and thus changes
that to:
error: build failed: file `/etc/guix/signing-key.sec' should be secret (inaccessible to everybody else)!
* nix/nix-daemon/nix-daemon.cc (performOp): Wrap 'exportPath' call in
'try' block.
Co-authored-by: Ludovic Courtès <ludo@gnu.org>