Send poltergeist presence update reusing previous presences.

If we do not reuse previous presences we lose avatar and name and people joining after the poltergeist creation will not be updated with those values.

resources/prosody-plugins/mod_muc_poltergeist.lua

 	return not not room:get_occupant_jid(poltergeist_component.."/"..nick);
 end
 
+-- Returns the last presence of occupant
+-- @param room the room instance where to check for occupant
+-- @param nick the nick of the occupant
+-- @return presence of the occupant
+function get_presence(room, nick)
+    local occupant_jid
+        = room:get_occupant_jid(poltergeist_component.."/"..nick);
+    if (occupant_jid) then
+        return room:get_occupant_by_nick(occupant_jid):get_presence();
+    end
+
+    return nil;
+end
+
 -- Event handlers
 
 --- Note: mod_muc and some of its sub-modules add event handlers between 0 and -100,
 
     local nick = string.sub(username, 0, 8);
     if (have_poltergeist_occupant(room, nick)) then
-        local update_presence = st.presence({
-            to = room.jid.."/"..nick,
-            from = poltergeist_component.."/"..nick
-        }):tag("status"):text(status):up();
+        local update_presence = get_presence(room, nick);
+
+        if (not update_presence) then
+            -- no presence found for occupant, create one
+            update_presence = st.presence({
+                to = room.jid.."/"..nick,
+                from = poltergeist_component.."/"..nick
+            });
+        else
+            -- update occupant presence with appropriate to and from
+            -- so we can send it again
+            update_presence = st.clone(update_presence);
+            update_presence.attr.to = room.jid.."/"..nick;
+            update_presence.attr.from = poltergeist_component.."/"..nick;
+        end
+
+        local once = false;
+        -- the status tag we will attach
+        local statusTag = st.stanza("status"):text(status);
+
+        -- if there is already a status tag replace it
+        update_presence:maptags(function (tag)
+            if tag.name == statusTag.name then
+                if not once then
+                    once = true;
+                    return statusTag;
+                else
+                    return nil;
+                end
+            end
+            return tag;
+        end);
+        if (not once) then
+            -- no status tag was repleced, attach it
+            update_presence:add_child(statusTag);
+        end
 
         room:handle_normal_presence(
             prosody.hosts[poltergeist_component], update_presence);