don't modify topIndex in handleTextChanged if control has not the focus

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

@@ -6046,7 +6046,7 @@ void handleTextChanged(TextChangedEvent event) {
 	}
 	int firstLine = content.getLineAtOffset(lastTextChangeStart);
 	resetCache(firstLine, 0);
-	if (!isFixedLineHeight() && topIndex > firstLine) {
+	if (!isFixedLineHeight() && isFocusControl() && topIndex > firstLine) {
 		topIndex = firstLine;
 		if (topIndex < 0) {
 			// TODO: This logging is in place to determine why topIndex is getting set to negative values.