Better handling of invalid coordinates

src/FlightMap/MapItems/MissionItemIndicatorDrag.qml

@@ -23,6 +23,7 @@ Rectangle {
     height:         _itemIndicatorHeight + (_touchMarginVertical * 2)
     color:          "transparent"
     z:              QGroundControl.zOrderMapItems + 1    // Above item icons
+    visible:        itemCoordinate.isValid
 
     // Properties which must be specific by consumer
     property var mapControl     ///< Map control which contains this item

src/FlightMap/MapItems/MissionLineView.qml

@@ -24,6 +24,6 @@ MapItemView {
         line.color: "#be781c"                           // Hack, can't get palette to work in here
         z:          QGroundControl.zOrderWaypointLines
 
-        path: object ? [ object.coordinate1, object.coordinate2 ] : [ ]
+        path: object && object.coordinate1.isValid && object.coordinate2.isValid ? [ object.coordinate1, object.coordinate2 ] : []
     }
 }