title: md autocomplete shows no results when input is empty
body: <p>I am using a md-autocomplete element, but there is no dropdown when the search field is empty. It doesn't even call the querySearch function. When I type anything the function is triggered and the autocomplete works. What am I doing wrong?</p>
  
  <p>The HTML:</p>
  
  <pre><code>        &lt;md-autocomplete
              md-selected-item="selectedItem"
              md-no-cache="true"
              md-search-text="searchText"
              md-items="item in querySearch(searchText)"
              md-item-text="item.name"
              placeholder="Select a Product"&gt;
                &lt;span md-highlight-text="searchText"&gt;
                   {{ '{{item.originalName}}  ({{item.id}})' }}
                &lt;/span&gt;
          &lt;/md-autocomplete&gt;
  </code></pre>
  
  <p>The JavaScript:</p>
  
  <pre><code>        function querySearch(query) {
              var results = query ? $scope.products.filter(createFilterFor(query)) : $scope.products;
              return results;
          }
  
  
          function createFilterFor(query) {
              var lowercaseQuery = angular.lowercase(query);
  
              return function filterFn(item) {
                  return (angular.lowercase(item.originalName).indexOf(lowercaseQuery) === 0);
              };
  
          }
  </code></pre>