[shotwell] Piwigo: Fix logging in with "&" in password

[Jens Georg <jensgeorg src gnome org>]

commit 48afdfd157bf835dd17a4b24aa46499216c866ec
Author: Jens Georg <mail+gitkraken jensge org>
Date:   Sat Mar 31 13:50:00 2018 +0200

    Piwigo: Fix logging in with "&" in password
    
    https://bugzilla.gnome.org/show_bug.cgi?id=718742

 plugins/shotwell-publishing/PiwigoPublishing.vala |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/plugins/shotwell-publishing/PiwigoPublishing.vala 
b/plugins/shotwell-publishing/PiwigoPublishing.vala
index 15d118b..fcd0aee 100644
--- a/plugins/shotwell-publishing/PiwigoPublishing.vala
+++ b/plugins/shotwell-publishing/PiwigoPublishing.vala
@@ -1643,8 +1643,8 @@ internal class SessionLoginTransaction : Transaction {
         base.with_endpoint_url(session, url);
 
         add_argument("method", "pwg.session.login");
-        add_argument("username", username);
-        add_argument("password", password);
+        add_argument("username", Uri.escape_string(username));
+        add_argument("password", Uri.escape_string(password));
     }
 
     public SessionLoginTransaction.from_other (Session session, Transaction other) {