OCI_ObjectToText() and OCI_CollToText() are mangling string conversion errors when using OCI_ENV_CONTEXT

[vrogier]

Whenever an error occurs in OCI_ObjectToText() and OCI_CollToText(), the library error handler is called (if set in OCI_Initialize() or using OCI_SetErrorHandler()).
But when using library flag OCI_ENV_CONTEXT, allowing usage of OCI_GetLastError(), a NULL OCI_Error handle is returned by OCI_GetLastError() in such cases.
Leading the C++ API to not throw C++ exception.

Whenever an error occurs in OCI_ObjectToText() and OCI_CollToText(), expected behavior is:

• OCI_GetLatError() shall return a valid OCI_Error handle when using OCI_ENV_CONTEXT flag
• ocilib::Object::ToString() and ocilib::Collection shall throw an C++ exception