fix: field boundary checks

Make sure field boundary detection always started, even
if the vehicle is driving to the field (and not started
on the field)

Also gracefully fail self unload without field polygon.

#861

Author: Peter Vaiko

scripts/ai/SelfUnloadHelper.lua

@@ -35,6 +35,10 @@ SelfUnloadHelper.maxDistanceFromField = 20
 ---@return table|nil best fill node of trailer
 ---@return number|nil distance of trailer from myVehicle
 function SelfUnloadHelper:findBestTrailer(fieldPolygon, myVehicle, implementWithPipe, pipeOffsetX)
+    if fieldPolygon == nil or #fieldPolygon == 0 then
+        CpUtil.errorVehicle(myVehicle, 'Field polygon is nil or empty, can\'t find a trailer to unload to')
+        return nil
+    end
     local bestTrailer, bestFillUnitIndex, bestFillType
     local minDistance = math.huge
     for _, otherVehicle in pairs(g_currentMission.vehicleSystem.vehicles) do
@@ -125,7 +129,6 @@ end
 ---@param fillRootNode number|nil optional fill node for the trailer, must not be nil if bestTrailer is not nil
 function SelfUnloadHelper:getTargetParameters(fieldPolygon, myVehicle, implementWithPipe, objectWithPipeAttributes,
                                               bestTrailer, fillRootNode)
-
     if not bestTrailer then
         -- no trailer passed in, let's find one
         bestTrailer, fillRootNode = SelfUnloadHelper:findBestTrailer(fieldPolygon, 

scripts/ai/strategies/AIDriveStrategyCombineCourse.lua

@@ -76,10 +76,6 @@ AIDriveStrategyCombineCourse.isAAIDriveStrategyCombineCourse = true
 function AIDriveStrategyCombineCourse:init(task, job)
     AIDriveStrategyFieldWorkCourse.init(self, task, job)
     AIDriveStrategyCourse.initStates(self, AIDriveStrategyCombineCourse.myStates)
-    --- Combine needs a field polygon for the self-unload to work. Although it is a user setting, but it can be
-    --- changed during the work, so we always require the field polygon, regardless of the setting, as it is checked
-    --- only after starting the CP driver.
-    self.state = self.states.WAITING_FOR_FIELD_BOUNDARY_DETECTION
     self.fruitLeft, self.fruitRight = 0, 0
     self.litersPerMeter = 0
     self.litersPerSecond = 0
@@ -243,17 +239,20 @@ function AIDriveStrategyCombineCourse:getDriveData(dt, vX, vY, vZ)
         self:setMaxSpeed(0)
     end
 
-    if self.state == self.states.INITIAL and self.vehicle:cpGetFieldPolygon() == nil then
-        self:setMaxSpeed(0)
-        self.state = self.states.WAITING_FOR_FIELD_BOUNDARY_DETECTION
+    --- Combine may need the field polygon for the self-unload to work, so if by now we don't have one
+    --- and the field boundary detection is not running, start it. This can happen if the combine wasn't started
+    --- directly, such as as it was driving to the field and then switched strategy
+    if not self.vehicle:cpIsFieldBoundaryDetectionRunning() and self.vehicle:cpGetFieldPolygon() == nil then
         self:startFieldBoundaryDetection()
     end
 
-    if self.state == self.states.WAITING_FOR_FIELD_BOUNDARY_DETECTION then
-        self:setMaxSpeed(0)
+    if self.vehicle:cpIsFieldBoundaryDetectionRunning() then
+        if self.settings.selfUnload:getValue() then
+            -- don't have the field boundary yet, and self unload is selected, don't move
+            self:setMaxSpeed(0)
+        end
         if self:waitForFieldBoundary() then
             self:debug('Have field boundary now.')
-            self.state = self.states.INITIAL
         end
     elseif self.state == self.states.WORKING then
         -- Harvesting