gtk3, gtk4: specify min-width only for discrete level bar blocks

For the block inside a LevelBar, apply the min-width property only when it is in discrete mode, so it is more visually accurate when the value results in a bar shorter than min-width.

Test program, Gtk4

import gi
gi.require_version("Gtk", "4.0")
from gi.repository import Gtk


class MainApplication(Gtk.Application):
    def __init__(self):
        super().__init__(application_id='org.gtk.Example')
        self.connect('activate', self.on_activate)
        self.interval = 2

    def init_window(self):
        self.win = Gtk.ApplicationWindow(application=self)
        self.grid = Gtk.Grid()
        self.win.set_default_size(300, 0)
        self.win.set_child(self.grid)

        self.bar = Gtk.LevelBar()
        self.bar.props.value = 2
        self.bar.props.max_value = 40

        self.btn = Gtk.Button()
        self.btn.props.label = f"increase by {self.interval}"

        self.label = Gtk.Label()
        self.update_label()

        self.btn.connect('clicked', lambda _: self.incr(self.interval))
        self.bar.connect('notify', lambda _, __: self.update_label())
        self.grid.attach(self.bar, 0, 0, 2, 1)
        self.grid.attach(self.btn, 0, 1, 1, 1)
        self.grid.attach(self.label, 1, 1, 1, 1)

    def incr(self, value):
        self.bar.props.value += value

    def update_label(self):
        self.label.props.label = f"current value: {self.bar.props.value:02.0f}"

    def on_activate(self, _):
        self.init_window()
        self.win.present()


app = MainApplication()
app.run(None)

Test program, Gtk3

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import Gtk


class MainApplication(Gtk.Application):
    def __init__(self):
        super().__init__(application_id='org.gtk.Example')
        self.connect('activate', self.on_activate)
        self.interval = 2

    def init_window(self):
        self.win = Gtk.ApplicationWindow(application=self)
        self.grid = Gtk.Grid()
        self.win.set_default_size(300, 0)
        self.win.add(self.grid)

        self.bar = Gtk.LevelBar()
        self.bar.props.value = 2
        self.bar.props.max_value = 40

        self.btn = Gtk.Button()
        self.btn.props.label = f"increase by {self.interval}"

        self.label = Gtk.Label()
        self.update_label()

        self.btn.connect('clicked', lambda _: self.incr(self.interval))
        self.bar.connect('notify', lambda _, __: self.update_label())
        self.grid.attach(self.bar, 0, 0, 2, 1)
        self.grid.attach(self.btn, 0, 1, 1, 1)
        self.grid.attach(self.label, 1, 1, 1, 1)

    def incr(self, value):
        self.bar.props.value += value

    def update_label(self):
        self.label.props.label = f"current value: {self.bar.props.value:02.0f}"

    def on_activate(self, _):
        self.init_window()
        self.win.show_all()


app = MainApplication()
app.run(None)

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