[FIRRTL] memory parsing crashes on unexpected order of "fields"

[dtzSiFive]

Consider:

FIRRTL version 4.0.0

circuit Foo:
  public module Foo:
    mem memory:
      depth => 8
      reader => r
      read-latency => 0
      write-latency => 1
      read-under-write => undefined
      data-type => UInt<8>

Which presently crashes. Moving data-type to the first (above depth => 8), and this works. In the current code is must occur before a port (e.g., reader).

If not supported, this should be rejected / checked.