Yardage - Fix broken display in 2.16

[PabstMirror]

Fix #9891
Before the code would spam 74210 cutText ["", "PLAIN"]; each frame
which should be valid, but it does create a new display each time
for some reason the onUnload of the last display would run after the onLoad of the new display
(apparently fixed in profiling branch)

Normal 2.16.151618:
[ACE] (yardage450) TRACE: 2198 before cut: (uiNamespace getVariable "ACE_RscYardage450")=any z\ace\addons\yardage450\functions\fnc_turnOn.sqf:46
"""onLoad"""
[ACE] (yardage450) TRACE: 2198 after cut: (uiNamespace getVariable "ACE_RscYardage450")=Display #-1 z\ace\addons\yardage450\functions\fnc_turnOn.sqf:50

[ACE] (yardage450) TRACE: 2226 before cut: (uiNamespace getVariable "ACE_RscYardage450")=Display #-1 z\ace\addons\yardage450\functions\fnc_turnOn.sqf:46
"""onLoad"""
"""onUnload""" // notice the order, this does `ACE_RscYardage450 = displayNull;`
[ACE] (yardage450) TRACE: 2226 after cut: (uiNamespace getVariable "ACE_RscYardage450")=No display z\ace\addons\yardage450\functions\fnc_turnOn.sqf:50

Profiling 2.16.151648:
[ACE] (yardage450) TRACE: 1325 before cut: (uiNamespace getVariable "ACE_RscYardage450")=any z\ace\addons\yardage450\functions\fnc_turnOn.sqf:46
"""onLoad"""
[ACE] (yardage450) TRACE: 1325 after cut: (uiNamespace getVariable "ACE_RscYardage450")=Display #-1 z\ace\addons\yardage450\functions\fnc_turnOn.sqf:50

[ACE] (yardage450) TRACE: 1353 before cut: (uiNamespace getVariable "ACE_RscYardage450")=Display #-1 z\ace\addons\yardage450\functions\fnc_turnOn.sqf:46
"""onUnload"""
"""onLoad"""
[ACE] (yardage450) TRACE: 1353 after cut: (uiNamespace getVariable "ACE_RscYardage450")=Display #-1 z\ace\addons\yardage450\functions\fnc_turnOn.sqf:50

[johnb432]

I was going to suggest isNil "__dsp", but realised that it's a macro...

All macros should be renamed to be upper case - I'll do it in another PR though.