[OpenMP][OMPT] Add two missing nullpointer checks in ompt-multiplex.h

In the functions ompt_multiplex_get_own_ompt_data and ompt_multiplex_get_client_ompt_data in addition to data being NULL, also the void pointer field "ptr" of "data" could be NULL, leading to a subsequent segfault. This patch add the corresponding checks. Patch prepared by Semih Burak Differential Revision: https://reviews.llvm.org/D112806

Author: jprotze

openmp/tools/multiplex/ompt-multiplex.h

@@ -142,6 +142,8 @@ static void ompt_multiplex_free_data_pair(ompt_data_t *data_pointer) {
 static ompt_data_t *ompt_multiplex_get_own_ompt_data(ompt_data_t *data) {
  if (!data)
  return NULL;
+ if (!data->ptr)
+ return NULL;
  ompt_multiplex_data_pair_t *data_pair =
  (ompt_multiplex_data_pair_t *)data->ptr;
  return &(data_pair->own_data);
@@ -150,6 +152,8 @@ static ompt_data_t *ompt_multiplex_get_own_ompt_data(ompt_data_t *data) {
 static ompt_data_t *ompt_multiplex_get_client_ompt_data(ompt_data_t *data) {
  if (!data)
  return NULL;
+ if (!data->ptr)
+ return NULL;
  ompt_multiplex_data_pair_t *data_pair =
  (ompt_multiplex_data_pair_t *)data->ptr;
  return &(data_pair->client_data);