[partition] Convenience for selecting default mount point

- map blank to the "(no mount point)" string for UI purposes

src/modules/partition/gui/EditExistingPartitionDialog.cpp

@@ -56,13 +56,12 @@ EditExistingPartitionDialog::EditExistingPartitionDialog( Device* device, Partit
     , m_usedMountPoints( usedMountPoints )
 {
     m_ui->setupUi( this );
-    standardMountPoints( *(m_ui->mountPointComboBox) );
+    standardMountPoints( *(m_ui->mountPointComboBox), PartitionInfo::mountPoint( partition ) );
 
     QColor color = ColorUtils::colorForPartition( m_partition );
     m_partitionSizeController->init( m_device, m_partition, color );
     m_partitionSizeController->setSpinBox( m_ui->sizeSpinBox );
 
-    m_ui->mountPointComboBox->setCurrentText( PartitionInfo::mountPoint( partition ) );
     connect( m_ui->mountPointComboBox, &QComboBox::currentTextChanged,
              this, &EditExistingPartitionDialog::checkMountPointSelection );
 

src/modules/partition/gui/MountPoints.cpp

@@ -46,3 +46,12 @@ standardMountPoints(QComboBox& combo)
     combo.addItems( standardMountPoints() );
 }
 
+void
+standardMountPoints(QComboBox& combo, const QString& selected)
+{
+    standardMountPoints( combo );
+    if ( selected.isEmpty() )
+        combo.setCurrentIndex( 0 );
+    else
+        combo.setCurrentText( selected );
+}

src/modules/partition/gui/MountPoints.h

@@ -38,4 +38,10 @@ QStringList standardMountPoints();
  */
 void standardMountPoints( QComboBox& );
 
+/**
+ * As above, but also sets the displayed mount point to @p selected,
+ * unless it is empty, in which case "(no mount point)" is chosen.
+ */
+void standardMountPoints( QComboBox&, const QString& selected );
+
 #endif