Don't print cuts between empty blocks in pretty printer

[seantalts]

stanc3/src/middle/Program.ml

Lines 117 to 129 in 8c999a5

	pp_functions_block (pp_fun_def pp_s) ppf prog ;
	Fmt.cut ppf () ;
	pp_input_vars pp_e ppf prog ;
	Fmt.cut ppf () ;
	pp_prepare_data pp_s ppf prog ;
	Fmt.cut ppf () ;
	pp_log_prob pp_s ppf prog ;
	Fmt.cut ppf () ;
	pp_generate_quantities pp_s ppf prog ;
	Fmt.cut ppf () ;
	pp_transform_inits pp_s ppf prog ;
	Fmt.cut ppf () ;
	pp_output_vars pp_e ppf prog ;