Fix #7687, fix crashing from bad error message argument

[scriptkittie]

What this does

This prevents an exception being thrown if 'msg' from print_error is nil by checking if msg is nil before attempting to work with 'msg'.

Fix #7687

Verification

• Start with a Windows XP SP3 box or VM for the victim.
• In attacking machine, start msfconsole
• DO: use use exploit/multi/handler
• DO: set payload windows/meterpreter/reverse_tcp
• DO: set LHOST [IP]
• DO: set LHOST [PORT]
• DO: setg SessionLogging true
• DO: run
• DO: sysinfo in meterpreter session.
• You should see no error logs if there is no session information. If there are session logs they will be displayed.
• The application will not crash if a bad 'msg' is passed to print_error.

[tdoan-r7]

Release Notes

This fix prevents an exception being thrown if 'msg' from print_error is nil by checking if msg is nil before attempting to work with 'msg'.