Fix a horrible scoping/associativity bug.

`1 as $x | . | $x` didn't compile, as it was parsed as

    (1 as $x | .) | $x

where `$x` is undefined, rather than as

    1 as $x | (. | $x)

testdata

@@ -146,6 +146,10 @@ null
 [6]
 [7]
 
+42 as $x | . | . | . + 432 | $x + 1
+34324
+43
+
 1 as $x | [$x,$x,$x as $x | $x]
 null
 [1,1,1]