[PATCH] SwitchMarketOrder error

[elexis]

This error occured when a player was defeated with r18581:

ERROR: JavaScript error: simulation/components/UnitAI.js line 5222
TypeError: this.order is undefined
  UnitAI.prototype.SwitchMarketOrder@simulation/components/UnitAI.js:5222:1
  Trader.prototype.SwitchMarket@simulation/components/Trader.js:260:3
  Mirage.prototype.UpdateTraders@simulation/components/Mirage.js:182:3
  Mirage.prototype.OnVisibilityChanged@simulation/components/Mirage.js:196:3

Not sure if it's that, but noone investigated this case yet as far as I know:

2016-06-03-QuakeNet-#0ad-dev.log:22:17 <@leper> another possible issue with that commit: what happens if one of the markets changes owner right before the trade is done?

[elexis]

Error occurs on turn 9015

[elexis]

• How can we reproduce the bug? Was it related to that comment?
• Perhaps there could be some test that ensures that a trade cart has no more work orders after ownership change etc.?
• This one hunk could become return this.MoveToPoint(point.x, point.z)) || this.MoveToMarket(targetMarket)

[mimo]

Sorry, I edited previous elexis post instead of replying to it :)

[elexis]

In 18749:

Fix a trade cart UnitAI error occuring rarely on defeat, by clearing the traderoute if the trader changed ownership. Patch by mimo, fixes #4131.

Also simplify MoveToMarket.

[elexis]

Thanks for the patch mimo! Sorry that we couldn't get to review this sooner.