join: "support" field numbers larger than usize::MAX

They silently get folded to usize::MAX, which is the official GNU behavior.

tests/fixtures/join/out_of_bounds_fields.expected

@@ -0,0 +1,25 @@
+ 1 2 c 1 cd
+ 1 3 d 2 de
+ 1 5 e 3 ef
+ 1 7 f 4 fg
+ 1 11 g 5 gh
+ 2 2 c 1 cd
+ 2 3 d 2 de
+ 2 5 e 3 ef
+ 2 7 f 4 fg
+ 2 11 g 5 gh
+ 3 2 c 1 cd
+ 3 3 d 2 de
+ 3 5 e 3 ef
+ 3 7 f 4 fg
+ 3 11 g 5 gh
+ 5 2 c 1 cd
+ 5 3 d 2 de
+ 5 5 e 3 ef
+ 5 7 f 4 fg
+ 5 11 g 5 gh
+ 8 2 c 1 cd
+ 8 3 d 2 de
+ 8 5 e 3 ef
+ 8 7 f 4 fg
+ 8 11 g 5 gh