mpi/c: check for valid datatype in file_get_type_extend

the interface if file_get_type_extent did not check
whether the input datatype is valid or not.

Makes the e_get_type_extend_2 test from the ibm testsuite pass.

Signed-off-by: Edgar Gabriel <egabriel@central.uh.edu>

ompi/mpi/c/file_get_type_extent.c

@@ -54,7 +54,10 @@ int MPI_File_get_type_extent(MPI_File fh, MPI_Datatype datatype,
             fh = MPI_FILE_NULL;
         } else if (NULL == extent) {
             rc = MPI_ERR_ARG;
+        } else {
+            OMPI_CHECK_DATATYPE_FOR_SEND(rc, datatype, 1);
         }
+
         OMPI_ERRHANDLER_CHECK(rc, fh, rc, FUNC_NAME);
     }