dbus: increase refcount on all signal handler candidates before iterating
dbus: increase refcount on all signal handler candidates before iterating

Calling a watcher handler might result in another watcher still in the
list becoming unref'd and destroyed but still dangling in the candidates
list. Increasing the refcount of all candidates keeps them alive until
handled.

Invalid read of size 4
   at 0x41CEEC3: _big_dbus_signal_watch_filter_message (dbus-signals.c:530)
   by 0x4C01A36: dbus_connection_dispatch (in /usr/lib/libdbus-1.so.3.4.0)
   by 0x508E59C: (within /usr/lib/libdbus-glib-1.so.2.1.0)
   by 0x4A59CF5: g_main_context_dispatch (in /usr/lib/libglib-2.0.so.0.1600.6)
   by 0x4A5D0B2: (within /usr/lib/libglib-2.0.so.0.1600.6)
   by 0x4A5D496: g_main_loop_run (in /usr/lib/libglib-2.0.so.0.1600.6)
   by 0x80489B7: main (main.c:82)
 Address 0x60cc874 is 12 bytes inside a block of size 44 free'd
   at 0x402265C: free (vg_replace_malloc.c:323)
   by 0x4A61B80: g_free (in /usr/lib/libglib-2.0.so.0.1600.6)
   by 0x41CE5E3: signal_watcher_unref (dbus-signals.c:95)
   by 0x41CE91E: big_dbus_unwatch_signal_by_id (dbus-signals.c:872)
   by 0x5B1EC92: big_js_dbus_unwatch_signal_by_id (dbus.c:707)
   by 0x4B4F37F: js_Invoke (jsinterp.c:1304)
   by 0x4B4222B: js_Interpret (jsinterp.c:4877)
   by 0x4B4F3CE: js_Invoke (jsinterp.c:1320)
   by 0x4B3D519: fun_apply (jsfun.c:1678)
   by 0x4B442AC: js_Interpret (jsinterp.c:4860)
   by 0x4B4F3CE: js_Invoke (jsinterp.c:1320)
   by 0x4B3D519: fun_apply (jsfun.c:1678)

endlessm/gjs,joeshaw/gjs,pixunil/cjs,joeshaw/gjs,mtwebster/cjs,mtwebster/cjs,magcius/gjs,joeshaw/gjs,joeshaw/gjs,joeshaw/gjs,djdeath/gjs,magcius/gjs,magcius/gjs,mtwebster/cjs,pixunil/cjs,pixunil/cjs,magcius/gjs,mtwebster/cjs,endlessm/gjs,pixunil/cjs,djdeath/gjs,magcius/gjs,djdeath/gjs,endlessm/gjs,pixunil/cjs,djdeath/gjs,endlessm/gjs,djdeath/gjs,mtwebster/cjs,endlessm/gjs