PlanManager: fix mission download progress

By adding a member variable for the total mission item count, we can
actually correctly estimate the progress.

src/MissionManager/PlanManager.cc

@@ -30,6 +30,7 @@ PlanManager::PlanManager(Vehicle* vehicle, MAV_MISSION_TYPE planType)
     , _transactionInProgress(TransactionNone)
     , _resumeMission(false)
     , _lastMissionRequest(-1)
+    , _missionItemCountToRead(-1)
     , _currentMissionIndex(-1)
     , _lastCurrentIndex(-1)
 {
@@ -317,6 +318,7 @@ void PlanManager::_handleMissionCount(const mavlink_message_t& message)
         for (int i=0; i<missionCount.count; i++) {
             _itemIndicesToRead << i;
         }
+        _missionItemCountToRead = missionCount.count;
         _requestNextMissionItem();
     }
 }
@@ -460,7 +462,7 @@ void PlanManager::_handleMissionItem(const mavlink_message_t& message, bool miss
         return;
     }
 
-    emit progressPct((double)seq / (double)_missionItems.count());
+    emit progressPct((double)seq / (double)_missionItemCountToRead);
     
     _retryCount = 0;
     if (_itemIndicesToRead.count() == 0) {

src/MissionManager/PlanManager.h

@@ -144,6 +144,7 @@ protected:
     QList<int>          _itemIndicesToWrite;    ///< List of mission items which still need to be written to vehicle
     QList<int>          _itemIndicesToRead;     ///< List of mission items which still need to be requested from vehicle
     int                 _lastMissionRequest;    ///< Index of item last requested by MISSION_REQUEST
+    int                 _missionItemCountToRead;///< Count of all mission items to read
     
     QList<MissionItem*> _missionItems;          ///< Set of mission items on vehicle
     QList<MissionItem*> _writeMissionItems;     ///< Set of mission items currently being written to vehicle