abuild: check early for signing keys

fi the signing key is missing we will fail. Rather than fail after
compile we check existance of signing keys before we start.

abuild.in

@@ -1185,6 +1185,8 @@ build_abuildrepo() {
 		_build=true
 	fi
 	if ! apk_up2date || [ -n "$force" ]; then
+		# check early if we have abuild key
+		abuild-sign --installed || return 1
 		logcmd "building $pkgname"
 		sanitycheck && builddeps && clean && fetch && unpack \
 			&& prepare && mkusers && $_build && rootpkg \