Don't fail if SYSTOOLS.GENERATE_SPREADSHEET is empty

When SYSTOOLS.GENERATE_SPREADSHEET returns an empty table it fails with an SQL State VSP05 and Vendor Code -438.

Modify the function to don't fail when it happens.

Example:

VALUES SYSTOOLS.GENERATE_SPREADSHEET(
  PATH_NAME =>'/home/csvtest',

  SPREADSHEET_QUERY =>'SELECT * FROM QSYS2.ASP_INFO WHERE ASP_NUMBER > 1',
  COLUMN_HEADINGS =>'COLUMN')

What I get:

SQL0438	Message GENERATE_SPREADSHEET: FAILED WITH SQLCODE=-438 SQLSTATE=VSP05 MESSAGE=GENERATE_SPREADSHEET: ACS - cldownload FAILED - CONSULT JOBLOG FOR DETAILS returned from SIGNAL, RESIGNAL, or RAISE_ERROR.

 Cause . . . . . :   An application has executed a SIGNAL or RESIGNAL statement, the RAISE_ERROR function has been invoked, or an error was signalled within a MERGE statement. If the application is an SQL procedure, function, trigger, or a compound (dynamic) statement, the SQLSTATE was not handled in the SQL routine.  The message returned is GENERATE_SPREADSHEET: FAILED WITH SQLCODE=-438 SQLSTATE=VSP05 MESSAGE=GENERATE_SPREADSHEET: ACS - cldownload FAILED - CONSULT JOBLOG FOR DETAILS. 

 Recovery  . . . :   See the documentation for the application that issued the SIGNAL or RESIGNAL statement or invoked the RAISE_ERROR function.

What I suggest:

No error and maybe the result of the function is 0 (-1 for error, 1 for successfull and 0 for empty)