Free the credentials iterator as well

Otherwise it gets leaked:

[356645.511913] systemd[1]: Stopping polkit.service - Authorization Manager...
[356645.514024] polkitd[15468]: Handling SIGTERM
[356645.514024] polkitd[15468]: Shutting down
[356645.519238] polkitd[15468]: Exiting with code 0
[356645.618456] polkitd[15468]: =================================================================
[356645.618456] polkitd[15468]: ==15468==ERROR: LeakSanitizer: detected memory leaks
[356645.618456] polkitd[15468]: Direct leak of 4000 byte(s) in 50 object(s) allocated from:
[356645.619128] polkitd[15468]:     #0 0x0000004a1a33 in malloc (/usr/lib/polkit-1/polkitd+0x4a1a33) (BuildId: a927b98f2ddc1b57773bec4e0f8a537fe46632b1)
[356645.619128] polkitd[15468]:     #1 0x7f1b20324039 in g_malloc (/lib64/libglib-2.0.so.0+0x47039) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #2 0x7f1b2033d4d4 in g_slice_alloc (/lib64/libglib-2.0.so.0+0x604d4) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #3 0x7f1b2036b547 in g_variant_iter_new (/lib64/libglib-2.0.so.0+0x8e547) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #4 0x7f1b2036dc5d  (/lib64/libglib-2.0.so.0+0x90c5d) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #5 0x7f1b2036d8b7  (/lib64/libglib-2.0.so.0+0x908b7) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #6 0x7f1b2036de0f in g_variant_get_va (/lib64/libglib-2.0.so.0+0x90e0f) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #7 0x7f1b2036df88 in g_variant_get (/lib64/libglib-2.0.so.0+0x90f88) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619128] polkitd[15468]:     #8 0x7f1b2067ce85 in polkit_system_bus_name_get_creds_sync /root/polkit/build/../src/polkit/polkitsystembusname.c:542:3
[356645.619128] polkitd[15468]:     #9 0x7f1b2067c997 in polkit_system_bus_name_get_process_sync /root/polkit/build/../src/polkit/polkitsystembusname.c:629:8
[356645.619128] polkitd[15468]:     #10 0x0000005069af in polkit_backend_session_monitor_get_session_for_subject /root/polkit/build/../src/polkitbackend/polkitbackendsessionmonitor-systemd.c:365:41
[356645.619128] polkitd[15468]:     #11 0x0000004f11b5 in polkit_backend_interactive_authority_revoke_temporary_authorization_by_id /root/polkit/build/../src/polkitbackend/polkitbackendinteractiveauthority.c:3567:24
[356645.619128] polkitd[15468]:     #12 0x0000004ea2c8 in server_handle_revoke_temporary_authorization_by_id /root/polkit/build/../src/polkitbackend/polkitbackendauthority.c:1292:8
[356645.619128] polkitd[15468]:     #13 0x0000004e805c in server_handle_method_call /root/polkit/build/../src/polkitbackend/polkitbackendauthority.c:1346:5
[356645.619128] polkitd[15468]:     #14 0x7f1b20565195  (/lib64/libgio-2.0.so.0+0xd9195) (BuildId: d06dc1cc6f8ddbb3cda89ef05ecf83d6fe037ae7)
[356645.619332] polkitd[15468]:     #15 0x7f1b20323e5c  (/lib64/libglib-2.0.so.0+0x46e5c) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619332] polkitd[15468]:     #16 0x7f1b2031d60b  (/lib64/libglib-2.0.so.0+0x4060b) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619332] polkitd[15468]:     #17 0x7f1b2037db37  (/lib64/libglib-2.0.so.0+0xa0b37) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619332] polkitd[15468]:     #18 0x7f1b203236f6 in g_main_loop_run (/lib64/libglib-2.0.so.0+0x466f6) (BuildId: c18bb9dc5295ff894f6098fa33e9ba39341c5bc1)
[356645.619332] polkitd[15468]:     #19 0x0000004e3619 in main /root/polkit/build/../src/polkitbackend/polkitd.c:298:3
[356645.619332] polkitd[15468]:     #20 0x7f1b1fe59447 in __libc_start_call_main (/lib64/libc.so.6+0x3447) (BuildId: f3ac204eaa4ceed81438c80e80998209f828bb1a)
[356645.619332] polkitd[15468]:     #21 0x7f1b1fe5950a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x350a) (BuildId: f3ac204eaa4ceed81438c80e80998209f828bb1a)
[356645.619332] polkitd[15468]:     #22 0x000000401c04 in _start (/usr/lib/polkit-1/polkitd+0x401c04) (BuildId: a927b98f2ddc1b57773bec4e0f8a537fe46632b1)
...

Follow-up for 8cabb11.

src/polkit/polkitsystembusname.c

@@ -566,6 +566,7 @@ polkit_system_bus_name_get_creds_sync (PolkitSystemBusName           *system_bus
     }
 
   g_variant_unref (result);
+  g_variant_iter_free (iter);
 
   if (out_uid)
     *out_uid = uid;