"panic: invalid memory address or nil pointer dereference" when quiet() is part of join assignment

[philrz]

Repro is with GA Zed tagged v1.15.0.

To repro, use attached Test data and conn.zng.gz and http.zng.gz with the following Zed script add-geo-to-http.zed:

file http.zng.gz
| inner join (
  file conn.zng.gz
  | head 100
  | _path=="conn"
) on uid=uid geo:=quiet(geo)

The panic:

$ zq -version
Version: v1.15.0

$ zq -I add-geo-to-http.zed 
panic: runtime error: invalid memory address or nil pointer dereference
goroutine 1 [running]:
runtime/debug.Stack()
	/usr/local/opt/[email protected]/libexec/src/runtime/debug/stack.go:24 +0x5e
github.com/brimdata/zed/runtime/sam/op.(*Catcher).Pull.func1()
	/Users/phil/work/zed/runtime/sam/op/catcher.go:25 +0x3d
panic({0x24052c0?, 0x3652d70?})
	/usr/local/opt/[email protected]/libexec/src/runtime/panic.go:914 +0x21f
github.com/brimdata/zed/runtime/sam/op/join.(*Op).buildType(0xc00057c820, 0xc0005ec180, 0x0)
	/Users/phil/work/zed/runtime/sam/op/join/join.go:226 +0x32
github.com/brimdata/zed/runtime/sam/op/join.(*Op).combinedType(0xc00057c820, 0xc0005ec180, 0x0)
	/Users/phil/work/zed/runtime/sam/op/join/join.go:242 +0x7f
github.com/brimdata/zed/runtime/sam/op/join.(*Op).splice(0xc00057c780?, {{0x28c64b0?, 0xc0005ec180?}, 0xc000e92140?, 0xc00049d740?}, {{0x28c6528?, 0xc00014c540?}, 0x3596538?, 0xc000154780?})
	/Users/phil/work/zed/runtime/sam/op/join/join.go:253 +0x1ab
github.com/brimdata/zed/runtime/sam/op/join.(*Op).Pull(0xc00057c820, 0x5?)
	/Users/phil/work/zed/runtime/sam/op/join/join.go:131 +0x538
github.com/brimdata/zed/runtime/sam/op.(*Single).Pull(0xc00014c5e8, 0x20)
	/Users/phil/work/zed/runtime/sam/op/mux.go:134 +0x2b
github.com/brimdata/zed/runtime/sam/op.(*Catcher).Pull(0x3cbf5b8?, 0x0?)
	/Users/phil/work/zed/runtime/sam/op/catcher.go:28 +0x62
github.com/brimdata/zed/runtime/exec.(*Query).Pull(0x4ab82f58?, 0xd8?)
	/Users/phil/work/zed/runtime/exec/query.go:59 +0x3e
github.com/brimdata/zed/zbuf.CopyPuller({0x4ab82f58, 0xc0005b9548}, {0x28c0220, 0xc00011b920})
	/Users/phil/work/zed/zbuf/batch.go:162 +0x4d
github.com/brimdata/zed/cli/zq.(*Command).Run(0xc0004c2a80, {0xc000040740, 0x0, 0x0})
	/Users/phil/work/zed/cli/zq/command.go:162 +0x79e
github.com/brimdata/zed/pkg/charm.path.run({0xc0006a8300?, 0x1, 0x1}, {0xc000040740?, 0x0, 0x0?})
	/Users/phil/work/zed/pkg/charm/path.go:11 +0x79
github.com/brimdata/zed/pkg/charm.(*Spec).ExecRoot(0x100874b?, {0xc000040730, 0x2, 0x2})
	/Users/phil/work/zed/pkg/charm/charm.go:63 +0x3f
main.main()
	/Users/phil/work/zed/cmd/zq/main.go:11 +0x5b

I originally wrote the Zed without the quiet() wrapper and caused the crash once I added it.