Fix crash caused by invalid text document layout.

Task-number: QTCREATORBUG-15955
Change-Id: I917bf0cc8921fe9dd40f8f58894a5c72e80441ed
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/texteditor/texteditor.cpp

@@ -4766,12 +4766,15 @@ void TextEditorWidgetPrivate::updateCurrentLineInScrollbar()
         m_highlightScrollBar->removeHighlights(Constants::SCROLL_BAR_CURRENT_LINE);
         if (m_highlightScrollBar->maximum() > 0) {
             const QTextCursor &tc = q->textCursor();
+            if (QTextLayout *layout = tc.block().layout()) {
                 const int lineNumberInBlock =
-                    tc.block().layout()->lineForTextPosition(tc.positionInBlock()).lineNumber();
-            m_highlightScrollBar->addHighlight(Constants::SCROLL_BAR_CURRENT_LINE,
+                        layout->lineForTextPosition(tc.positionInBlock()).lineNumber();
+                m_highlightScrollBar->addHighlight(
+                            Constants::SCROLL_BAR_CURRENT_LINE,
                             q->textCursor().block().firstLineNumber() + lineNumberInBlock);
             }
         }
+    }
 }
 
 void TextEditorWidgetPrivate::slotUpdateBlockNotify(const QTextBlock &block)