STK: Image/icon related fixes

1. Handle invalid images/icons
If the coding scheme of the image is not understood, then the
loading of the icon will fail.
Send a TR with ResultCode.PRFRMD_ICON_NOT_DISPLAYED back to
the card when this happens, but continue processing the command.

2. For Idle Mode Text the icon should be loaded even when text
is not present

Change-Id: Ie4199fe9ac00f14db2d6b12604fc2c9cf54208f5