ShellAgent should catch java.security.AccessControlException as well when handling file access requests

[notthetup]

Currently, the ShellAgent specifically catches IOExceptions when handling file access requests (GetFileReq, PutFileReq).

 try {
      if (f.isDirectory()) {
      ....
    } catch (IOException ex) {
      log.warning(ex.toString());
    } finally {
     ...

However, accessing files can also throw AccessControlException if a Java Security Policy is in place. If those aren't caught at this level, the MessageBehaviour crashes and is removed from the ShellAgent. So the Agent can't respond to any more messages.

1632115867860|WARNING|org.arl.fjage.shell.ShellAgent/yoda@33:executeBehavior|Exception in agent: websh

For example, doing a GetFileReq on a file file-without-permissions.txt to which JVM doesn't have permissions based on the security policy will return this error.

1632115867860|WARNING|org.arl.fjage.shell.ShellAgent/yoda@33:executeBehavior|Exception in agent: websh

java.security.AccessControlException: access denied ("java.io.FilePermission" "file-without-permissions.txt" "read")
Stack trace: ...
   org.arl.fjage.shell.ShellAgent.handleGetFileReq(ShellAgent.java:551)
   org.arl.fjage.shell.ShellAgent.access$500(ShellAgent.java:26)
   org.arl.fjage.shell.ShellAgent$3.onReceive(ShellAgent.java:251)
   org.arl.fjage.MessageBehavior.action(MessageBehavior.java:142)
   org.arl.fjage.Agent.executeBehavior(Agent.java:781)
   org.arl.fjage.Agent.run(Agent.java:818) ...

After this error, no other GetFileReq/PutFileReq get any responses.