Unhelpful error message from parse_area_file if file not found

Code Sample, a minimal, complete, and verifiable piece of code

from pyresample.area_config import parse_area_file
parse_area_file("filenotfound")

Problem description

This fails with an AttributeError. This wasted me some time as I thought that the problem was with the contents of the yaml-file or elsewhere.

Expected Output

I'd like to see this raise a FileNotFoundError.

Actual Result, Traceback if applicable

Traceback (most recent call last):
  File "mwe6.py", line 2, in <module>
    parse_area_file("filenotfound")
  File "/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/pyresample/area_config.py", line 104, in parse_area_file
    return _parse_yaml_area_file(area_file_name, *regions)
  File "/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/pyresample/area_config.py", line 139, in _parse_yaml_area_file
    area_dict = _read_yaml_area_file_content(area_file_name)
  File "/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/pyresample/area_config.py", line 123, in _read_yaml_area_file_content
    area_dict = recursive_dict_update(area_dict, tmp_dict)
  File "/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/pyresample/utils/__init__.py", line 231, in recursive_dict_update
    for k, v in u.items():
AttributeError: 'str' object has no attribute 'items'

Versions of Python, package at hand and relevant dependencies

Python 3.7.3, pyresample 1.13.2.

Start in pyresample/area_config.py at parse_area_file, then follow _parse_yaml_area_file to _read_yaml_area_file_content and the recursive_dict_update call. Reproduce the missing-file example from the issue and verify that parse_area_file raises FileNotFoundError instead of the reported AttributeError.