Delay the initialization until necessary.

Signed-off-by: George Bosilca <bosilca@icl.utk.edu>

opal/datatype/opal_datatype.h

@@ -81,7 +81,6 @@ BEGIN_C_DECLS
                                           OPAL_DATATYPE_FLAG_DATA |       \
                                           OPAL_DATATYPE_FLAG_COMMITTED)
 
-
 /**
  * The number of supported entries in the data-type definition and the
  * associated type.
@@ -349,13 +348,13 @@ static inline ptrdiff_t
 opal_datatype_span( const opal_datatype_t* pData, int64_t count,
                     ptrdiff_t* gap)
 {
-    ptrdiff_t extent = (pData->ub - pData->lb);
-    ptrdiff_t true_extent = (pData->true_ub - pData->true_lb);
     if (OPAL_UNLIKELY(0 == pData->size) || (0 == count)) {
         *gap = 0;
         return 0;
     }
     *gap = pData->true_lb;
+    ptrdiff_t extent = (pData->ub - pData->lb);
+    ptrdiff_t true_extent = (pData->true_ub - pData->true_lb);
     return true_extent + (count - 1) * extent;
 }