Setting "Socket Timeout" or "Stop Context Timeout" to 0 in mod_cluster configuration yields "Unknown error"

Description of problem:
Setting "Socket Timeout" or "Stop Context Timeout" to 0 in mod_cluster configuration yields "Unknown error"

Version-Release number of selected component (if applicable):
6.3.0.ER9

How reproducible:
always

Steps to Reproduce:
1. start EAP server in standalone-full-ha
2. go to http://localhost:9990/console/App.html#modcluster
3. set "Socket Timeout" or "Stop Context Timeout" in "Networking" tab to 0

Actual results:
Unknown error message

Expected results:
Explanation/warning of invalid setting.