gdkevents-win32.c: Use g_strdup() in gdk_settings_notify()

Hi,

When starting GTK+ programs on CJK (Chinese, Japanese, Korean) Windows, the IM context code (hence the IME support code) will be activated automatically, so it is both unecessary (and causing crashes) to send a gtk-im-module settings change event afterwards in gdkevents-win32.c when we, say, for instance, change from a Chinese input method to a Korean input method (or vice-versa), or when we activate any IME input method when one is not activated yet.

With blessings, thank you!