QLineF: Don't try calculating a unit vector when length is null

It's undefined and causes a division by zero.

Fixes: oss-fuzz-24561
Pick-to: 5.12 5.15
Change-Id: Idebaba4b286e3ab0ecb74825d203244958ce6aec
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/auto/corelib/tools/qline/tst_qline.cpp b/tests/auto/corelib/tools/qline/tst_qline.cpp
index 4f3be0f3d9..7e07e9d1e2 100644
--- a/tests/auto/corelib/tools/qline/tst_qline.cpp
+++ b/tests/auto/corelib/tools/qline/tst_qline.cpp
@@ -40,6 +40,8 @@ private slots:
     void testLength();
     void testLength_data();
 
+    void testSetLength();
+
     void testCenter();
     void testCenter_data();
 
@@ -258,6 +260,15 @@ void tst_QLine::testLength()
     QCOMPARE(l.dy(), qreal(vy));
 }
 
+void tst_QLine::testSetLength()
+{
+    QLineF l(0, 0, 4e-323, 5e-324);
+    const qreal newLength = 1892;
+    const qreal oldLength = l.length();
+    l.setLength(newLength);
+    QCOMPARE(l.length(), oldLength ? newLength : 0);
+}
+
 void tst_QLine::testCenter()
 {
     QFETCH(int, x1);