pxyconn.c: fix double free of host and serv variables

[disaykin]

When -1 is returned from sys_sockaddr_str, pointers in *host
and *serv are invalid and must not be used nor freed by the caller

[sonertari]

This is complicated. Because,

1. We actually zero out ctx, so normally those are already NULL.
2. I am not sure what happens in the case of protocol changes, such as passthrough mode. Because I am not sure if the code reaches there again (do we reinit logging?). And if it does reach there again, those are not NULL, and the fix you suggested would cause memory leak.

[sonertari]

I guess we should actually fix sys_sockaddr_str().

[disaykin]

I agree. Thanks.

[sonertari]

Thanks.