No FIRRTL parsing error on malformed input

[seldridge]

The following malformed FIRRTL snippet parses just fine, but leads to a very unintuitive error later on. Here, a user forgets to indent a line in a module. This seems to kill parsing and you wind up with a likely downstream error of no top module being found.

circuit Foo:
  module Bar:
    input a: UInt<1>
output b: UInt<1>
    b <- a

  module Foo:
    input a: UInt<1>
    output b: UInt<1>
    inst bar of Bar
    bar.a <- a
    b <- bar.b

./utils/bin/firrtl -i Foo.fir

Exception in thread "main" firrtl.passes.CheckHighFormLike$NoTopModuleException: : A single module must be named Foo, but no modules have that name.
	at firrtl.passes.CheckHighFormLike.run(Checks.scala:235)
	at firrtl.passes.CheckHighFormLike.run$(Checks.scala:71)
	at firrtl.passes.CheckChirrtl.run(CheckChirrtl.scala:17)

Type of issue: bug report

If the current behavior is a bug, please provide the steps to reproduce the problem:

See example above.

• Please tell us about your environment:
  master

What is the use case for changing the behavior?

Impact: no functional change

Development Phase: request