Fix no values case to draw correct grid (#3686 An error occurred )

src/MissionEditor/MissionItemStatus.qml

@@ -38,10 +38,10 @@ Rectangle {
     property real   _gradientPercent:   isNaN(_gradient) ? 0 : _gradient * 100
     property real   _azimuth:           _statusValid ? _currentMissionItem.azimuth : -1
     property bool   _statusValid:       currentMissionItem != undefined
-    property string _distanceText:      _statusValid ? QGroundControl.metersToAppSettingsDistanceUnits(_distance).toFixed(2) + " " + QGroundControl.appSettingsDistanceUnitsString : ""
-    property string _altText:           _statusValid ? QGroundControl.metersToAppSettingsDistanceUnits(_altDifference).toFixed(2) + " " + QGroundControl.appSettingsDistanceUnitsString : ""
-    property string _gradientText:      _statusValid ? _gradientPercent.toFixed(0) + "%" : ""
-    property string _azimuthText:       _statusValid ? Math.round(_azimuth) : ""
+    property string _distanceText:      _statusValid ? QGroundControl.metersToAppSettingsDistanceUnits(_distance).toFixed(2) + " " + QGroundControl.appSettingsDistanceUnitsString : " "
+    property string _altText:           _statusValid ? QGroundControl.metersToAppSettingsDistanceUnits(_altDifference).toFixed(2) + " " + QGroundControl.appSettingsDistanceUnitsString : " "
+    property string _gradientText:      _statusValid ? _gradientPercent.toFixed(0) + "%" : " "
+    property string _azimuthText:       _statusValid ? Math.round(_azimuth) : " "
 
     readonly property real _margins:    ScreenTools.defaultFontPixelWidth