instance_ext.rs: Use ObjectExt::connect() instead of the unsafe bindings

Close #42
Status Job ID Name Coverage
  Test
passed #152847
nightly:test

00:03:44

 
  Lint
failed #152848
rustfmt

00:00:17

 
Name Stage Failure
failed
rustfmt Lint
+    flags: c_int,
+ fields: *const GLogField,
+ nr_fields: size_t,
+ user: gpointer,
+) -> c_int;

extern "C" {
// fn g_log_set_always_fatal(flags: ::libc::c_int) -> ::libc::c_int;
ERROR: Job failed: exit code 1