[577134] Changed modifier check to allow arrow key scrolling

With this fix scrolling with arrow key is now only possible when no
modifier key is pressed.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=577134
Change-Id: I5178bae011b9942a2a761432632487358c169b31

plugins/org.eclipse.fordiac.ide.gef/src/org/eclipse/fordiac/ide/gef/handlers/AdvancedGraphicalViewerKeyHandler.java

@@ -20,13 +20,13 @@
 public class AdvancedGraphicalViewerKeyHandler extends GraphicalViewerKeyHandler {
 	private static final int SCROLL_SPEED = 400;
 
-	public AdvancedGraphicalViewerKeyHandler(AdvancedScrollingGraphicalViewer viewer) {
+	public AdvancedGraphicalViewerKeyHandler(final AdvancedScrollingGraphicalViewer viewer) {
 		super(viewer);
 	}
 
 	@Override
-	public boolean keyPressed(KeyEvent event) {
-		boolean modifierPressed = (event.stateMask & SWT.MODIFIER_MASK) == 0;
+	public boolean keyPressed(final KeyEvent event) {
+		final boolean modifierPressed = (event.stateMask & SWT.MODIFIER_MASK) != 0;
 		switch (event.keyCode) {
 		case SWT.ARROW_DOWN:
 			if (!modifierPressed) {