Disable the "Start" scan button when the "--Select Site--" option is selected

[GoogleCodeExporter]

Steps to reproduce the issue:
1. Run ZAP;
2. Access a site;
3. Select the "Active Scan" tab and choose the accessed site;
4. Choose the "--Select Site--" option and note that the "Start Active scan" 
button is still enabled;

Remarks:
Pressing the "Start" button starts the scan on the last selected site.
The issue happens with the following footer panels:
 - "Active scan";
 - "Spider";
 - "Forced Browse";
 - "Port Scan" (option "--Select Host--").

ZAP Version:
Version 2.0.0 (and trunk r3029).

Original issue reported on code.google.com by THC...@gmail.com on 9 Apr 2013 at 2:54

[GoogleCodeExporter]

r4516

zap-extensions beta branch:
https://code.google.com/p/zap-extensions/source/detail?r=1082

Original comment by THC...@gmail.com on 28 Mar 2014 at 3:06

• Changed state: Committed

[GoogleCodeExporter]

Original comment by psii...@gmail.com on 31 Mar 2014 at 11:17

• Added labels: Build-20140327

[GoogleCodeExporter]

Fixed in ZAP 2.3.0

Original comment by psii...@gmail.com on 10 Apr 2014 at 3:25

• Changed state: Fixed