Null this in pgConn::GetStatus

pgadmin3-1.22.1

When compiled with gcc6, the evil practice of "this == 0" fails
horribly. The most obvious effect is crashing during startup. I've
attached a simple patch. The Fedora bugzilla is here:

https://bugzilla.redhat.com/show_bug.cgi?id=1335043

A detailed explanation of why this == 0 is evil:
http://www.viva64.com/en/b/0226/

The patch moves the guts of pgConn::GetStatus() to a static function,
where comparing the ptr arg to 0 is well defined, and makes the
GetStatus() member function call the static function inline. It is
still technically undefined when calling the GetStatus member function
on a null ptr - but for now the compiler is not eliminating the test.
It is also a step in right direction, which would be to use the static
function at calling sites where the ptr could be null.