fix bug 21723

https://gna.org/bugs/index.php?21723

The problem appears to be that when checking the team associated
to an item, we match it against the playing team rather than the
viewing team. This has the consequence that when it is not your
turn, you can see items that should only be visible to the
(opposing) side that is currently playing.

Tested that the bug is fixed using the following test scenario,
placed in data/multiplayer/scenarios:

    [multiplayer]
        name = "Unit Test item_visibility"
        map_data = "{test/maps/move_skip_sighted.map}"
        turns = 3
        id = item_visibility
        random_start_time = no

        {DAWN}

        [side]
            side=1
            controller=human
            name = "Alice"
            type = Elvish Archer
            id=alice
            fog=yes
            team_name=West
            share_view=no
        [/side]
        [side]
            side=2
            controller=human
            name = "Bob"
            type = Orcish Grunt
            id=bob
            fog=yes
            team_name=East
            share_view=no
        [/side]
        [side]
            side=3
            controller=human
            name = "Dave"
            type = Dwarvish Fighter
            id=dave
            fog=yes
            team_name=East
            share_view=no
        [/side]

        [event]
            name = prestart
            [item]
		x=2
		y=3
		image=scenery/rune1.png
		team_name=West
            [/item]
            [item]
		x=2
		y=5
		image=scenery/rune1.png
		team_name=East
            [/item]

            [label]
                x=3
                y=3
                text = "West team"
                team_name=West
            [/label]

            [label]
                x=3
                y=5
                text = "East team"
                team_name=East
            [/label]
        [/event]

    [/multiplayer]
Merge branch 'fixbug21723'
update changelog