desktop: avoid crashes on drag&drop in GroupedLineEdit

If the user manages to "scroll" through the QPlainTextEdit by
a drag&drop action, the state of the widget becomes inconsistent.
On the one hand, the text-block says that it has one line.
On the other hand, its layout says that it has no line.
When trying to fetch the line, a crash occurs.

Try to detect such a strange state and return early in
GroupedLineEdit::paintEvent().

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 9 insertions, 1 deletions

diff --git a/desktop-widgets/groupedlineedit.cpp b/desktop-widgets/groupedlineedit.cpp
index fdce55ca4..5639b2e1b 100644
--- a/desktop-widgets/groupedlineedit.cpp
+++ b/desktop-widgets/groupedlineedit.cpp
@@ -161,7 +161,15 @@ void GroupedLineEdit::keyPressEvent(QKeyEvent *e)
 
 void GroupedLineEdit::paintEvent(QPaintEvent *e)
 {
-	QTextLine line = document()->findBlock(0).layout()->lineAt(0);
+	// Do some sanity checks. Without these, the code may crash if
+	// the user manages to scroll the text box by drag&drop actions.
+	const QTextBlock &block = document()->findBlock(0);
+	if (block.lineCount() <= 0)
+		return QPlainTextEdit::paintEvent(e);
+	const QTextLayout *layout = block.layout();
+	if (layout->lineCount() <= 0)
+		return QPlainTextEdit::paintEvent(e);
+	QTextLine line = layout->lineAt(0);
 	QPainter painter(viewport());
 
 	painter.setRenderHint(QPainter::Antialiasing, true);