title: ag-grid's agSelectCellEditor doesn't render the cell correctly
body: <p>I am using agSelectCellEditor to imlement a dropdown menu in a particular column cells.
  This is the column definition:</p>
  
  <pre><code>{
        headerName: "Rattachement",
        field: "rattachement",
        editable: true,
        headerTooltip:
          "Choisissez l'entité de rattachement parmi les choix présents dans la liste déroulante",
        cellEditor: "agSelectCellEditor",
        cellEditorParams: {
          values: [
            "",
            "Audit",
            "RA",
            "Consulting",
            "FA",
            "Tax&amp;Legal",
            "ICS",
            "Taj"
          ]
        }
      }
  </code></pre>
  
  <p>This is how ag-grid renders it:<br>
  <a href="https://i.stack.imgur.com/HpQez.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HpQez.png" alt="enter image description here"></a><br>
  I have to doubl-click on it in order for the dropdown list to show-up this way:<br>
  <a href="https://i.stack.imgur.com/90HlN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/90HlN.png" alt="enter image description here"></a><br>
  And then I can select any of the available options.<br>
  As you notice, this is really poor rendering and may cause the user to be confused and unable to use the tool that I am building.  </p>
  
  <p>So my question is:</p>
  
  <p>Is there any way to make ag-grid show the dropdown menu from the beginnig without having to double-click on the cell so that the user actually knows what to do?<br>
  Thanks!  </p>
  
  <p>PS: I don't want to use a custom cell renderer, because the options in the cell depend on other variables and the whole thing may get messy if I choose to implement the dropdown list using a customcellRenderer (which I did with other columns where it doesn't cause me any of the mentioned trouble)</p>