Unable to find Enum in Instance when Imported
I'm not sure whether this is the right repository or not, feel free to move the issue.

Enums don't work when they are used under the condition, that they are
- used in an instance and 
-  are imported from another ksy-file.

I run Kaitai Struct locally in its WebIDE with latest commit `3a8cbe0d50596546fc05946bb27c6a04ec404ce9`.

See the following example which produces the error message for `bar` while `foo` works fine.
```
Parse error: undefined
Call stack: undefined io.kaitai.struct.precompile.ErrorInInput: (main): /types/bar/instances/get_some_value/value: unable to find enum 'my_enum::foo', searching from repreoducer::bar
```
My current workaround is to define the enum inside `reproducer.ksy` then it works fine.

reproducer.ksy
```ksy
meta:
  id: repreoducer
  file-extension: repreoducer
  endian: le
  imports: my_enum
  
types:

  foo:
    seq:
      - id: bitmap
        type: u2
        enum: my_enum::foo

  bar:
    seq:
      - id: bitmap
        type: u2
    instances:
      get_some_value:
        value: bitmap & 0x03
        enum: my_enum::foo
```

my_enum.ksy
```ksy
meta:
  id: my_enum
  file-extension: my_enum

enums:
  foo:
    0: test0
    1: test1
```

This might be related to #651 but it seems like this bug has already been fixed, at least my type `foo` works without any problems.