External references is not propagated

[ShouheiNishi]

In some case, external references is not propagated. So allOf generates broken code.

[ShouheiNishi]

Test code in https://github.com/ShouheiNishi/oapi-codegen/commit/635077fa443da80f9e49f0d2d98bdec82ce9b1c0

$ git status
HEAD detached at 635077f
nothing to commit, working tree clean
$ go generate ./internal/test/issues/issue-1202/...
$ go test ./internal/test/issues/issue-1202/...
# github.com/deepmap/oapi-codegen/internal/test/issues/issue-1202/pkg1
internal/test/issues/issue-1202/pkg1/pkg1.gen.go:10:12: undefined: TestObj3
?       github.com/deepmap/oapi-codegen/internal/test/issues/issue-1202/pkg2    [no test files]
FAIL
$

[matoous]

Seems to be duplicate of: https://github.com/oapi-codegen/oapi-codegen/issues/632.