Fix for disappearing and inaccurate buffer previews in adv labeling

src/app/qgslabelpreview.cpp

@@ -48,6 +48,10 @@ void QgsLabelPreview::paintEvent( QPaintEvent *e )
   p.setFont( font() );
   QFontMetrics fm( font() );
 
+  // otherwise thin buffers don't look like those on canvas
+  if ( mBufferSize != 0 && mBufferSize < 1 )
+    mBufferSize = 1;
+
   double xtrans = 0;
   if ( mBufferSize != 0 )
     xtrans = mBufferSize / 4;

src/app/qgslabelpreview.h

@@ -32,7 +32,7 @@ class QgsLabelPreview : public QLabel
     void paintEvent( QPaintEvent* e );
 
   private:
-    int mBufferSize;
+    double mBufferSize;
     QColor mBufferColor;
     Qt::PenJoinStyle mBufferJoinStyle;
     bool mBufferNoFill;