Disable up/down buttons upon dialog initialisation.

When initialising the ExplanationPreferencesGeneralPanel dialog, make
sure the "up" and "down" buttons are disabled if no row is selected in
the list of available explanation services (which is normally the case
when the dialog is created).

protege-editor-owl/src/main/java/org/protege/editor/owl/ui/explanation/ExplanationPreferencesGeneralPanel.java

@@ -94,6 +94,7 @@ private void addUpDownButtons(PreferencesLayoutPanel panel, JTable pluginTable)
 			}
 			pluginTable.setRowSelectionInterval(rowIndex - 1, rowIndex - 1);
 		});
+		buttonUp.setEnabled(pluginTable.getSelectedRow() != -1);
 
 		JButton buttonDown = new JButton("↓ Move down︎");
 		buttonDown.setToolTipText("Move the selected explanation service towards the bottom of the list");
@@ -104,6 +105,7 @@ private void addUpDownButtons(PreferencesLayoutPanel panel, JTable pluginTable)
 			}
 			pluginTable.setRowSelectionInterval(rowIndex + 1, rowIndex + 1);
 		});
+		buttonDown.setEnabled(pluginTable.getSelectedRow() != -1);
 
 		JPanel buttonsUpDown = new JPanel();
 		buttonsUpDown.add(buttonUp);