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.
