qemu: fix failure to start with spice graphics and no tls

qemu: fix failure to start with spice graphics and no tls

Commit eca3fdf inadvertantly caused a failure to start for any domain
with the following in its config:

    <graphics type='spice' autoport='yes'/>

The problem is that when tlsPort == 0 and defaultMode == "any" (which
is the default for defaultMode), this would be flagged in the code as
"needTLSPort", and if there was then no spice tls config, the new
error+fail would happen.

This patch checks for the case of defaultMode == "any", and in that
case simply doesn't allocate a TLS port (since that's probably not
what the user wanted, and it would have failed later anyway.). It does
leave the error in place for cases when the user specifically asked to
use tls in one way or another, though.