QVariant: Fix crash when comparing two variant with the same undefined type.

If the type is the same, but not registered, the returned string could be
null (or empty if a empty string was registered)
In that case, QVariant compare() function  would access invalid memory.

Protect against that case. qstrcmp returns 0 if 0 is given as a parametter.

Task-number: QTBUG-8700
Reviewed-by: Markus Goetz

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/auto/qvariant/tst_qvariant.cpp b/tests/auto/qvariant/tst_qvariant.cpp
index a316dda637..b7e2c81e98 100644
--- a/tests/auto/qvariant/tst_qvariant.cpp
+++ b/tests/auto/qvariant/tst_qvariant.cpp
@@ -1968,6 +1968,10 @@ void tst_QVariant::operator_eq_eq_data()
 
         QTest::newRow("HashSecondLarger") << QVariant(hash1) << QVariant(hash2) << false;
     }
+
+    QTest::newRow( "UserType" ) << QVariant(QVariant::UserType) << QVariant(QVariant::UserType) << false;
+    QVariant mUserType(QVariant::UserType);
+    QTest::newRow( "Shared UserType" ) << mUserType << mUserType << true;
 }
 
 void tst_QVariant::operator_eq_eq()