Only call close_pid in _finalize if it's open
Only call close_pid in _finalize if it's open

Apparently g_return_* family of functions is a debug tool that when hit
logs a critical warning before returning, so a public API mis-use safeguard,
not an allowed thing. Makes sense to keep it as g_return_* though and make
sure no warning happen, then we can G_DISABLE_CHECKS at some point later
for production builds.

leio/libdvbsub,leio/libdvbsub