build: Give a helpful error when the file to be built is not found

Recently something regressed which meant that when building a missing
file, the result was this long unhelpful traceback:

    2016-04-27 12:23:36 Deciding on task order
    Traceback (most recent call last):
      ...
      File "/src/morph/morphlib/sourceresolver.py", line 506, in create_source_pool
        definitions_original_ref=original_ref)
      File "/src/morph/morphlib/sourceresolver.py", line 440, in add_morphs_to_source_pool
        add_to_pool, predefined_split_rules)
      File "/src/morph/morphlib/sourceresolver.py", line 287, in _process_definitions_with_children
        morphology = get_morphology(filename)
      File "/src/morph/morphlib/sourceresolver.py", line 282, in get_morphology
        filename)
      File "/src/morph/morphlib/sourceresolver.py", line 255, in _get_morphology
        morph = morph_loader.load_from_string(text, filename)
      File "/src/morph/morphlib/morphloader.py", line 395, in load_from_string
        obj = yaml.safe_load(string)
    ...
      File "/usr/lib/python2.7/site-packages/yaml/reader.py", line 178, in update_raw
        data = self.stream.read(size)
    AttributeError: 'NoneType' object has no attribute 'read'

Now the error is:

    ERROR: Couldn't find definition file to build: missing-file.morph

Change-Id: Iabb315c9d0ac5c7c50003db36a1b21e86fb23223

0 files changed, 0 insertions, 0 deletions