[SofaPyhon3/Plugin] Fix regression introduced in PR #4243

To fix memory error in PR sofa-framework#243

There is the need to get the latest data by calling getValue().

The way it was done in the PR is wrong because it is using a begin/end edit pairs
which trigger the DDG's follower to notify the data is dirty (while it is not).

The consequence was that every call on read access eg:
print(myobjec.position.value)
was triggering the data change mecanisme

Author: damienmarchal

Plugin/src/SofaPython3/DataHelper.cpp

@@ -294,7 +294,7 @@ size_t getSize(BaseData* self)
 
 py::buffer_info toBufferInfo(BaseData& m)
 {
-    scoped_read_access guard(&m);
+    m.updateIfDirty();
 
     const AbstractTypeInfo& nfo { *m.getValueTypeInfo() };
     auto itemNfo = nfo.BaseType();