Avoid destroying all onboard units after player upgrade Air Carrier unit. (#8129)

core/src/com/unciv/logic/map/MapUnit.kt

@@ -916,17 +916,19 @@ class MapUnit : IsPartOfGameInfoSerialization {
         attacksSinceTurnStart.clear()
     }
 
-    fun destroy() {
+    fun destroy(destroyTransportedUnit: Boolean = true) {
         val currentPosition = Vector2(getTile().position)
         civInfo.attacksSinceTurnStart.addAll(attacksSinceTurnStart.asSequence().map { CivilizationInfo.HistoricalAttackMemory(this.name, currentPosition, it) })
         currentMovement = 0f
         removeFromTile()
         civInfo.removeUnit(this)
         civInfo.updateViewableTiles()
-        // all transported units should be destroyed as well
-        currentTile.getUnits().filter { it.isTransported && isTransportTypeOf(it) }
-            .toList() // because we're changing the list
-            .forEach { unit -> unit.destroy() }
+        if (destroyTransportedUnit) {
+            // all transported units should be destroyed as well
+            currentTile.getUnits().filter { it.isTransported && isTransportTypeOf(it) }
+                .toList() // because we're changing the list
+                .forEach { unit -> unit.destroy() }
+        }
         isDestroyed = true
     }
 

core/src/com/unciv/ui/worldscreen/unit/UnitActions.kt

@@ -446,7 +446,7 @@ object UnitActions {
         return UnitAction(UnitActionType.Upgrade,
             title = title,
             action = {
-                unit.destroy()
+                unit.destroy(destroyTransportedUnit = false)
                 val newUnit = civInfo.placeUnitNearTile(unitTile.position, upgradedUnit.name)
 
                 /** We were UNABLE to place the new unit, which means that the unit failed to upgrade!