opensc-tool: only show the card name if present, to avoid "(null)"

[martinpaljak]

Before:

$ opensc-tool -lv
Nr.  Card  Features  Name
0    No              FujitsuTechnologySolutions GmbH SmartCase KB SCR eSIG [SmartCase Smartcard Reader] 00 00
1    Yes             ACS ACR 38U-CCID 01 00
     3b:6e:00:00:80:31:80:66:b0:84:0c:01:6e:01:83:00:90:00 (null)

After:

$ opensc-tool -lv
Nr.  Card  Features  Name
0    No              FujitsuTechnologySolutions GmbH SmartCase KB SCR eSIG [SmartCase Smartcard Reader] 00 00
1    Yes             ACS ACR 38U-CCID 01 00
     3b:6e:00:00:80:31:80:66:b0:84:0c:01:6e:01:83:00:90:00

Change-Id: Id2cb858897cd845d93609e28019c94736b04fa93