If called on an empty collection, don't let OEnumerationByIndex.nextElement()

call XIndexAccess.getByIndex() with an invalid index, just like
OEnumerationByName.nextElement() doesn't.

Patch by: me

comphelper/source/container/enumhelper.cxx

@@ -188,14 +188,13 @@ staruno::Any SAL_CALL OEnumerationByIndex::nextElement(  )
     ::osl::ResettableMutexGuard aLock(m_aLock);
 
     staruno::Any aRes;
-    if (m_xAccess.is())
-    {
+    if (m_xAccess.is() && m_nPos < m_xAccess->getCount())
         aRes = m_xAccess->getByIndex(m_nPos++);
-        if (m_nPos >= m_xAccess->getCount())
-        {
-            impl_stopDisposeListening();
-            m_xAccess.clear();
-        }
+
+    if (m_xAccess.is() && m_nPos >= m_xAccess->getCount())
+    {
+        impl_stopDisposeListening();
+        m_xAccess.clear();
     }
 
     if (!aRes.hasValue())       // es gibt kein Element mehr