[Survey transects generation] introduce function to handle one polygon at a time

src/MissionManager/SurveyComplexItem.cc

@@ -1067,6 +1067,11 @@ void SurveyComplexItem::_rebuildTransectsPhase1(void)
 }
 
 void SurveyComplexItem::_rebuildTransectsPhase1Worker(bool refly)
+{
+    _rebuildTranscetsFromPolygon(refly);
+}
+
+void SurveyComplexItem::_rebuildTranscetsFromPolygon(bool refly)
 {
     if (_ignoreRecalc) {
         return;

src/MissionManager/SurveyComplexItem.h

@@ -111,6 +111,7 @@ private:
     bool _loadV3(const QJsonObject& complexObject, int sequenceNumber, QString& errorString);
     bool _loadV4(const QJsonObject& complexObject, int sequenceNumber, QString& errorString);
     void _rebuildTransectsPhase1Worker(bool refly);
+    void _rebuildTranscetsFromPolygon(bool refly); ///< Adds to the _transects array from one polygon
 
     QMap<QString, FactMetaData*> _metaDataMap;