[StickyScrolling] Avoid out of bound error when styling sticky lines

Fixes #2750

Author: Christopher-Hermann

bundles/org.eclipse.ui.editors/src/org/eclipse/ui/internal/texteditor/stickyscroll/StickyLine.java

@@ -53,6 +53,12 @@ public String getText() {
 	@Override
 	public StyleRange[] getStyleRanges() {
 		StyledText textWidget= sourceViewer.getTextWidget();
+		int widgetLineNumber = getWidgetLineNumber();
+
+		if (widgetLineNumber > textWidget.getLineCount()) {
+			return null;
+		}
+
 		int offsetAtLine= textWidget.getOffsetAtLine(getWidgetLineNumber());
 		StyleRange[] styleRanges= textWidget.getStyleRanges(offsetAtLine, getText().length());
 		for (StyleRange styleRange : styleRanges) {

tests/org.eclipse.ui.editors.tests/src/org/eclipse/ui/internal/texteditor/stickyscroll/StickyLineTest.java

@@ -14,6 +14,7 @@
 package org.eclipse.ui.internal.texteditor.stickyscroll;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 
 import org.junit.After;
 import org.junit.Before;
@@ -94,6 +95,16 @@ public void testGetStyleRanges() {
 		assertEquals(2, styleRanges[1].length);
 	}
 
+	@Test
+	public void testGetStyleRangesIgnoresOutOfBoundLines() {
+		textWidget.setText("line1\nline2\nline3");
+
+		StickyLine stickyLineOutOfBound = new StickyLine(10, sourceViewer);
+		StyleRange[] styleRanges = stickyLineOutOfBound.getStyleRanges();
+
+		assertNull(styleRanges);
+	}
+
 	@Test
 	public void WithSourceViewerLineMapping() {
 		sourceViewer = new SourceViewerWithLineMapping(shell, null, SWT.None);