Philippe 26/09/2017: IO: do not write GRID attribute if not useful (not set or set to 0)

src/LIB/SURCOUCHE/src/mode_netcdf.f90

@@ -215,7 +215,8 @@ ENDIF
 ! GRID attribute definition
 IF(TPFIELD%NGRID<0) THEN
   CALL PRINT_MSG(NVERB_DEBUG,'IO','IO_WRITE_FIELD_ATTR_NC4','TPFIELD%NGRID not set for variable '//TRIM(TPFIELD%CMNHNAME))
-ELSE
+!Do not write GRID attribute if NGRID=0
+  ELSE IF (TPFIELD%NGRID>0) THEN
   STATUS = NF90_PUT_ATT(KNCID, KVARID, 'GRID', TPFIELD%NGRID)
   IF (STATUS /= NF90_NOERR) CALL HANDLE_ERR(status,__LINE__,'IO_WRITE_FIELD_ATTR_NC4 [NF90_PUT_ATT]')
 ENDIF