QJniArray: add missing post-increment operator

Augment test case. Found during header review.

Task-number: QTBUG-119952
Change-Id: I326395397167edb05ff1f45f7151614c02b7e7eb
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit e5074cd3540e165f771aa5bfea36d09553eadc77)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qjniarray.h

@@ -50,6 +50,12 @@ struct QJniArrayIterator
         ++that.m_index;
         return that;
     }
+    friend QJniArrayIterator operator++(QJniArrayIterator &that, int) noexcept
+    {
+        auto copy = that;
+        ++that;
+        return copy;
+    }
 
     void swap(QJniArrayIterator &other) noexcept
     {

tests/auto/corelib/kernel/qjniarray/tst_qjniarray.cpp

@@ -92,6 +92,17 @@ void tst_QJniArray::operators()
     QJniArray<jbyte> array(bytes);
     QVERIFY(array.isValid());
 
+    {
+        auto it = array.begin();
+        QCOMPARE(*it, 'a');
+        QCOMPARE(*++it, 'b');
+        QCOMPARE(*it++, 'b');
+        QCOMPARE(*it, 'c');
+        ++it;
+        it++;
+        QCOMPARE(*it, 'e');
+        QCOMPARE(++it, array.end());
+    }
     {
         QJniArray<jbyte>::const_iterator it = {};
         QCOMPARE(it, QJniArray<jbyte>::const_iterator{});