cdfDefVarMissval: write _FillValue on first timestep.

src/cdf_write.c

@@ -94,7 +94,8 @@ void cdfDefVarMissval(stream_t *streamptr, int varID, int dtype, int lcheck)
 
       if ( xtype == NC_BYTE && missval > 127 && missval < 256 ) xtype = NC_INT;
 
-      if ( streamptr->ncmode != 2 ||
+      if ( lcheck == 0 ||
+           streamptr->ncmode != 2 ||
            streamptr->filetype == CDI_FILETYPE_NC ||
            streamptr->filetype == CDI_FILETYPE_NC2 )
         cdf_put_att_double(fileID, ncvarid, "_FillValue", (nc_type) xtype, 1, &missval);