qt: Allow horizontal slider in debugwindow peers tab to autosize display

Not all possible node flags where visible since v18.2 with fixed size.
When size width from fixed 300 set to -1 or 0, qt will autosize the slider.

Signed-off-by: saibato <saibato.naga@pm.me>

src/qt/forms/debugwindow.ui

@@ -1080,7 +1080,7 @@
               </property>
               <property name="minimumSize">
                <size>
-                <width>300</width>
+                <width>0</width>
                 <height>0</height>
                </size>
               </property>