percentile value check can be slow

I tried to enter invalid percentile fractions, and was astonished that 
it seems to be checked after many work is done?

psql (11devel)
Type "help" for help.

jotpe=# \timing
Timing is on.
jotpe=# select percentile_cont(array[0,0.25,0.5,1,1,null,2]) within 
group(order by txk) from klima_tag;
ERROR:  percentile value 2 is not between 0 and 1
Time: 19155,565 ms (00:19,156)
jotpe=# select count(*) from klima_tag;  count
---------- 13950214
(1 row)

Time: 933,847 ms


Best regards Johannes