offload-build: return failure if no package files were found

This means that the remote command died at some stage earlier than the
printing of created files.

Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>

offload-build

@@ -116,4 +116,6 @@ if (( ${#files[@]} )); then
     printf '%s\n' '' '-> copying files...'
     load_makepkg_config
     scp "${files[@]/#/$server:}" "${PKGDEST:-${PWD}}/"
+else
+    exit 1
 fi