[core] Use _wnck_error_trap_push/pop instead of gdk_error_trap_push/pop
[core] Use _wnck_error_trap_push/pop instead of gdk_error_trap_push/pop

There was one instance where this was not the case.

lanoxx/libwnck,Sidnioulz/SandboxLibwnck,Sidnioulz/SandboxLibwnck,lanoxx/libwnck