[applets/digital-clock] Use -1 instead of undefined to unset font.pointSize

It's a bit more reliable in this case

applets/digital-clock/package/contents/ui/DigitalClock.qml

@@ -491,8 +491,8 @@ Item {
                     weight: plasmoid.configuration.boldText ? Font.Bold : PlasmaCore.Theme.defaultFont.weight
                     italic: plasmoid.configuration.italicText
                     pixelSize: 1024
-                    pointSize: undefined // Because we're setting the pixel size instead
-                                         // TODO: remove once this label is ported to PC3
+                    pointSize: -1 // Because we're setting the pixel size instead
+                                  // TODO: remove once this label is ported to PC3
                 }
                 minimumPixelSize: 1
 
@@ -518,8 +518,8 @@ Item {
                 font.weight: timeLabel.font.weight
                 font.italic: timeLabel.font.italic
                 font.pixelSize: 1024
-                font.pointSize: undefined // Because we're setting the pixel size instead
-                                          // TODO: remove once this label is ported to PC3
+                font.pointSize: -1 // Because we're setting the pixel size instead
+                                   // TODO: remove once this label is ported to PC3
                 minimumPixelSize: 1
 
                 visible: text.length > 0
@@ -537,8 +537,8 @@ Item {
             font.weight: timeLabel.font.weight
             font.italic: timeLabel.font.italic
             font.pixelSize: 1024
-            font.pointSize: undefined // Because we're setting the pixel size instead
-                                      // TODO: remove once this label is ported to PC3
+            font.pointSize: -1 // Because we're setting the pixel size instead
+                               // TODO: remove once this label is ported to PC3
             minimumPixelSize: 1
 
             horizontalAlignment: Text.AlignHCenter