Merge branch 'bugfix_streammgr_optierr' into release-v8.4.0 (PR #1441)

This merge fixes an issue within mpas_get_stream_filename() where the optional
argument ierr was being assigned to before checking if it was passed in.

The routine now checks if ierr is present, and if so initializes it to
MPAS_STREAM_MGR_NOERR.

* bugfix_streammgr_optierr:
  Fix premature use of optional argument in mpas_get_stream_filename

Author: mgduda

src/framework/mpas_stream_manager.F

@@ -4073,7 +4073,9 @@ subroutine mpas_get_stream_filename(manager, streamID, when, blockID, filename,
         type (MPAS_TimeInterval_type) :: filename_interval
         type (MPAS_Time_type) :: now_time
 
-        ierr = 0
+        if ( present(ierr) ) then
+           ierr = MPAS_STREAM_MGR_NOERR
+        end if
 
         if ( present(blockID) ) then
            blockID_local = blockID