codegen: Improve GValueModule.visit_cast_expression()
codegen: Improve GValueModule.visit_cast_expression()

Re-use the result of the GValue-getter invocation

frida/vala,frida/vala,frida/vala,GNOME/vala,frida/vala,GNOME/vala,GNOME/vala,GNOME/vala,frida/vala