Remove draggability of single control item (#295)

Author: ahmadayubi

src/mapml/layers/MapLayer.js

@@ -541,7 +541,7 @@ export var MapMLLayer = L.Layer.extend({
             // Fixes flickering by only moving element when there is enough space
             let offset = moveEvent.clientY - yPos;
             moving = Math.abs(offset) > 5 || moving;
-            if(controls && !moving || 
+            if( (controls && !moving) || (controls && controls.childElementCount <= 1) || 
                 controls.getBoundingClientRect().top > control.getBoundingClientRect().bottom || 
                 controls.getBoundingClientRect().bottom < control.getBoundingClientRect().top){
                   return;