Good reference identified as "part of a cycle of substitutions"

[zzhang97]

Describe the Bug

The following configuration snippet

base {
}

app = ${base} {
  a {
    b = 1
  }
  c = [
    ${app.a.b}
  ]
}

was complained as "${app.a.b} was part of a cycle of substitutions."

Expected Behavior

The above configuration is OK.

Steps to Reproduce

Steps to reproduce the behavior:

	auto config = hocon::config::parse_string(R"(
base {
}

app = ${base} {
  a {
    b = 1
  }
  c = [
    ${app.a.b}
  ]
}
)"
	)->resolve();

Environment

• Version [cpp-hocon 0.3.0]
• Platform [Ubuntu 18.04, g++ 10.3]