fix(ui-select): avoid dropdown flickering on search

setting the opacity to 0 on each call to calculateDropdownPos brought
the dropdown to flicker when you typed a search text. Now it is only
doing this on initially opening the dropdown which avoids a flickering
on the opening effect.

Author: m3co-code

Diff for: src/uiSelectDirective.js

@@ -295,6 +295,13 @@ uis.directive('uiSelect',
         scope.$watch('$select.open', function() {
 
           if ($select.dropdownPosition === 'auto' || $select.dropdownPosition === 'up'){
+            // Hide the dropdown to avoid flickering on initial opening
+            dropdown = angular.element(element).querySelectorAll('.ui-select-dropdown');
+
+            if (dropdown.length > 0) {
+              dropdown[0].style.opacity = 0;
+            }
+
             scope.calculateDropdownPos();
           }
 
@@ -331,9 +338,6 @@ uis.directive('uiSelect',
               return;
             }
 
-            // Hide the dropdown so there is no flicker until $timeout is done executing.
-            dropdown[0].style.opacity = 0;
-
             // Delay positioning the dropdown until all choices have been added so its height is correct.
             $timeout(function(){