Change KeyUp to KeyDown event so we don't get false positives. Refs #674

* If we pick up on keyup, it might be a keypress from somewhere else
  (like a dialog) that was released on our control. Instead we should
  look for keydown.

renderdocui/Windows/Dialogs/LiveCapture.cs

@@ -777,7 +777,7 @@ namespace renderdocui.Windows
             lastEdit = DateTime.Now;
         }
 
-        private void captures_KeyUp(object sender, KeyEventArgs e)
+        private void captures_KeyDown(object sender, KeyEventArgs e)
         {
             if (e.KeyCode == Keys.Delete)
             {