New functions to perform a precheck for the user data and metadata
parameters that are going to be used to execute a OBS_GetData operation.
Doing this before the OBD_GetData we are able to check if we're going to
have problems with the current request. Is useful because right now
we're using the *_Exception_Safe functions which return NULL in case we
have an exception, this leads to execute the whole request even if we
know beforehand that it's going to fail.
Mario de Frutos