Fixed a crash when disguising the spy as civilian in Allies04

Introduced by #4006

```
Exception of type `System.InvalidOperationException`: Unit `c1` does not have a sequence `stand2`
  at OpenRA.Graphics.SequenceProvider.GetSequence (System.String unitName, System.String sequenceName) [0x00043] in OpenRA.Game/Graphics/SequenceProvider.cs:55 
  at OpenRA.Graphics.Animation.PlayFetchIndex (System.String sequenceName, System.Func`1 func) [0x0002b] in OpenRA.Game/Graphics/Animation.cs:115 
  at OpenRA.Mods.RA.Render.RenderInfantry.Tick (OpenRA.Actor self) [0x00000] in <filename unknown>:0 
  at OpenRA.Mods.RA.RenderInfantryProne.Tick (OpenRA.Actor self) [0x00000] in <filename unknown>:0 
  at OpenRA.Mods.RA.Render.RenderSpy.Tick (OpenRA.Actor self) [0x00000] in <filename unknown>:0 
  at OpenRA.World.<Tick>m__181 (TraitPair`1 x) [0x0000e] in OpenRA.Game/World.cs:221 
  at (wrapper delegate-invoke) System.Action`1<OpenRA.TraitPair`1<OpenRA.Traits.ITick>>:invoke_void__this___T (OpenRA.TraitPair`1<OpenRA.Traits.ITick>)
  at OpenRA.WorldUtils+<DoTimed>c__AnonStorey7D`1[OpenRA.TraitPair`1[OpenRA.Traits.ITick]].<>m__187 (TraitPair`1 x) [0x00014] in OpenRA.Game/WorldUtils.cs:176 
  at OpenRA.Exts.Do[TraitPair`1] (IEnumerable`1 e, System.Action`1 fn) [0x00017] in OpenRA.FileFormats/Exts.cs:35 
  at OpenRA.WorldUtils.DoTimed[TraitPair`1] (IEnumerable`1 e, System.Action`1 a, System.String text, Double time) [0x00034] in OpenRA.Game/WorldUtils.cs:173 
  at OpenRA.World.Tick () [0x0013b] in OpenRA.Game/World.cs:221 
  at OpenRA.Game.TickInner (OpenRA.Network.OrderManager orderManager) [0x00135] in OpenRA.Game/Game.cs:201 
  at OpenRA.Game.Tick (OpenRA.Network.OrderManager orderManager) [0x00034] in OpenRA.Game/Game.cs:127 
  at OpenRA.Game.Run () [0x0006d] in OpenRA.Game/Game.cs:434 
  at OpenRA.Program.Run (System.String[] args) [0x00011] in OpenRA.Game/Support/Program.cs:114 
  at OpenRA.Program.Main (System.String[] args) [0x0005a] in OpenRA.Game/Support
```