apkbuild-cpan: fix handling of license meta-data

Don't update if it's unknown, and fix the error message.

apkbuild-cpan.in

@@ -249,8 +249,10 @@ sub do_depends {
 		$text =~ s/^pkgdesc=\"([^\"]*)\"$/pkgdesc=\"$abstract\"/mg or
 			die "Can't find cpandepends line in APKBUILD";
 	}
-	$text =~ s/^license=\"([^\"]*)\"$/license=\"$license\"/mg or
-		die "Can't find cpandepends line in APKBUILD";
+	if ($license ne 'unknown') {
+		$text =~ s/^license=\"([^\"]*)\"$/license=\"$license\"/mg or
+			die "Can't find license line in APKBUILD";
+	}
 	$text =~ s/^cpandepends=\"([^\"]*)\"$/cpandepends=\"$deps\"/mg or
 		die "Can't find cpandepends line in APKBUILD";
 	$text =~ s/^cpanmakedepends=\"([^\"]*)\"$/cpanmakedepends=\"$makedeps\"/mg or