show error message in case the author_name is not present

[rahulakrishna]

• Adds a check for author name and shows error message but continues
  execution with empty author name

Resolves: #25

[Mohan-cloud]

Apologies if this is not the right place to comment this. Running this latest commit produces the following error for me.

No author was found in clippings file. You can manually edit your clippings file to add Author in the format: <Title: (Lastname, Firstname)>. For now continuing with empty author name
Traceback (most recent call last):
File "/usr/lib/python3.9/runpy.py", line 197, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.9/runpy.py", line 87, in _run_code
exec(code, run_globals)
File "/home/abc/Documents/projects/kindle2notion/kindle2notion/main.py", line 31, in
main()
File "/home/abc/.local/share/virtualenvs/kindle2notion-bDmVw8vi/lib/python3.9/site-packages/click/core.py", line 1134, in call
return self.main(*args, **kwargs)
File "/home/abc/.local/share/virtualenvs/kindle2notion-bDmVw8vi/lib/python3.9/site-packages/click/core.py", line 1059, in main
rv = self.invoke(ctx)
File "/home/abc/.local/share/virtualenvs/kindle2notion-bDmVw8vi/lib/python3.9/site-packages/click/core.py", line 1401, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/abc/.local/share/virtualenvs/kindle2notion-bDmVw8vi/lib/python3.9/site-packages/click/core.py", line 767, in invoke
return __callback(*args, **kwargs)
File "/home/abc/Documents/projects/kindle2notion/kindle2notion/main.py", line 25, in main
books = parse_raw_clippings_text(all_clippings)
File "/home/abc/Documents/projects/kindle2notion/kindle2notion/parsing.py", line 18, in parse_raw_clippings_text
author, title = _parse_author_and_title(raw_clipping_list)
File "/home/abc/Documents/projects/kindle2notion/kindle2notion/parsing.py", line 36, in _parse_author_and_title
author, title = _deal_with_exceptions_in_author_name(author, title)
File "/home/abc/Documents/projects/kindle2notion/kindle2notion/parsing.py", line 84, in _deal_with_exceptions_in_author_name
last_name, first_name = author.split(', ')
ValueError: too many values to unpack (expected 2)