fix: make last(empty) yield no output values (#3179)

jq.1.prebuilt

@@ -3475,9 +3475,13 @@ The \fBnth(n; expr)\fR function extracts the nth value output by \fBexpr\fR\. No
 .
 .nf
 
-jq \'[first(range(\.)), last(range(\.)), nth(\./2; range(\.))]\'
+jq \'[first(range(\.)), last(range(\.)), nth(5; range(\.))]\'
    10
 => [0,9,5]
+
+jq \'[first(empty), last(empty), nth(5; empty)]\'
+   null
+=> []
 .
 .fi
 .