plugins/runcommand: set Dialog preferredWidth

The Add command dialog currently does not set a preferredWidth, which
seems to cause repeated binding loops and a lot of log spam until the
dialog is actually put on screen.

This change sets the preferredWidth to 20*gridUnit, which seems to be
the typical size used in small dialogs and is about the size that the
dialog has without a width explicitly set.

plugins/runcommand/kdeconnect_runcommand_config.qml

@@ -72,6 +72,7 @@ ListView {
         title: i18nc("@title:window", "Add Command")
 
         padding: Kirigami.Units.largeSpacing
+        preferredWidth: Kirigami.Units.gridUnit * 20
 
         property Kirigami.Action addCommandAction: Kirigami.Action {
             text: i18nc("@action:button", "Add")