use lineExists add 4 more locations

Author: tobias-melcher

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java

@@ -1087,15 +1087,15 @@ void calculateTopIndex(int delta) {
 				lineIndex++;
 			}
 			int lineHeight = 0;
-			if (lineIndex >= 0 && lineIndex < lineCount) {
+			if (lineExists(lineIndex)) {
 				lineHeight = renderer.getCachedLineHeight(lineIndex);
 			}
 			if (lineIndex < lineCount && -delta + lineHeight <= clientAreaHeight - topMargin - bottomMargin) {
 				topIndex = lineIndex;
 				topIndexY = -delta;
 			} else {
 				topIndex = lineIndex - 1;
-				if (topIndex >= 0 && topIndex < lineCount) {
+				if (lineExists(topIndex)) {
 					topIndexY = -renderer.getCachedLineHeight(topIndex);
 				}
 				topIndexY -= delta;
@@ -1106,15 +1106,15 @@ void calculateTopIndex(int delta) {
 			while (lineIndex > 0) {
 				int previousLineIndex = lineIndex - 1;
 				int lineHeight = 0;
-				if (previousLineIndex >= 0 && previousLineIndex < lineCount) {
+				if (lineExists(previousLineIndex)) {
 					lineHeight = renderer.getCachedLineHeight(previousLineIndex);
 				}
 				if (delta + lineHeight > 0) break;
 				delta += lineHeight;
 				lineIndex--;
 			}
 			int lineHeight = 0;
-			if (lineIndex >= 0 && lineIndex < lineCount) {
+			if (lineExists(lineIndex)) {
 				lineHeight = renderer.getCachedLineHeight(lineIndex);
 			}
 			if (lineIndex == 0 || -delta + lineHeight <= clientAreaHeight - topMargin - bottomMargin) {