Handle presence received before roster

Presence of contact not found in roster are filtered out.
But sometimes roster is received after a first few presences.

We choose to store presences until we receive roster and then process
this presences.

Fixes #1050

src/xmpp/roster_list.h

@@ -72,5 +72,6 @@ GSList* roster_get_contacts_by_presence(const char *const presence);
 char* roster_get_msg_display_name(const char *const barejid, const char *const resource);
 gint roster_compare_name(PContact a, PContact b);
 gint roster_compare_presence(PContact a, PContact b);
+void roster_process_pending_presence(void);
 
 #endif