Remove extraneous local variable in FileChooserDialog::with_buttons

This commit removes the `first_button_text` variable from
`FileChooserDialog::with_buttons`, as requested in the PR #602

Author: demurgos

src/file_chooser_dialog.rs

@@ -42,39 +42,36 @@ impl FileChooserDialog {
                     )
                 },
                 1 => {
-                    let first_button_text: Stash<*const c_char, str> = buttons[0].0.to_glib_none();
                     ffi::gtk_file_chooser_dialog_new(
                         title.to_glib_none().0,
                         parent.to_glib_none().0,
                         action.to_glib(),
-                        first_button_text.0,
+                        buttons[0].0.to_glib_none().0,
                         buttons[0].1.to_glib(),
                         ptr::null::<c_char>(),
                     )
                 },
                 2 => {
-                    let first_button_text: Stash<*const c_char, str> = buttons[0].0.to_glib_none();
                     let second_button_text: Stash<*const c_char, str> = buttons[1].0.to_glib_none();
                     ffi::gtk_file_chooser_dialog_new(
                         title.to_glib_none().0,
                         parent.to_glib_none().0,
                         action.to_glib(),
-                        first_button_text.0,
+                        buttons[0].0.to_glib_none().0,
                         buttons[0].1.to_glib(),
                         second_button_text.0,
                         buttons[1].1.to_glib(),
                         ptr::null::<c_char>(),
                     )
                 },
                 3 => {
-                    let first_button_text: Stash<*const c_char, str> = buttons[0].0.to_glib_none();
                     let second_button_text: Stash<*const c_char, str> = buttons[1].0.to_glib_none();
                     let third_button_text: Stash<*const c_char, str> = buttons[2].0.to_glib_none();
                     ffi::gtk_file_chooser_dialog_new(
                         title.to_glib_none().0,
                         parent.to_glib_none().0,
                         action.to_glib(),
-                        first_button_text.0,
+                        buttons[0].0.to_glib_none().0,
                         buttons[0].1.to_glib(),
                         second_button_text.0,
                         buttons[1].1.to_glib(),