client/gtk2: Fix a build failure with GDK_MODIFIER_INTENT_NO_TEXT_INPUT
client/gtk2: Fix a build failure with GDK_MODIFIER_INTENT_NO_TEXT_INPUT

BUG=https://github.com/ibus/ibus/issues/1942

Review URL: https://codereview.appspot.com/327300043

ibus/ibus,fujiwarat/ibus,fujiwarat/ibus,ibus/ibus,fujiwarat/ibus,ibus/ibus,ibus/ibus,fujiwarat/ibus