tweak is_patch_for function to make it more robust

[boegel]

Adding a patch file to a PR via --update-pr was sort of broken because the is_patch_for function wasn't robust enough.
There were two problematic cases:

1. An easyconfig for which components was set to None, which is the case for AOMP easyconfigs because the custom easyblock for AOMP uses None as default value for components:

(see details below for traceback)

Traceback (most recent call last):
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/kehoste/work/easybuild-framework/easybuild/main.py", line 597, in <module>
    main()
  File "/Users/kehoste/work/easybuild-framework/easybuild/main.py", line 510, in main
    update_pr(options.update_pr, categorized_paths, ordered_ecs)
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1924, in update_pr
    update_branch(branch_name, paths, ecs, github_account=github_account, commit_msg=commit_msg)
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1894, in update_branch
    _, _, _, _, diff_stat, pr_target_repo = _easyconfigs_pr_common(paths, ecs, start_branch=branch_name,
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 862, in _easyconfigs_pr_common
    patch_specs = det_patch_specs(paths['patch_files'], file_info, [target_dir])
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1060, in det_patch_specs
    soft_name = find_software_name_for_patch(patch_file, ec_dirs)
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1121, in find_software_name_for_patch
    if is_patch_for(patch_name, ec['ec']):
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1023, in is_patch_for
    for entry in itertools.chain(ec['exts_list'], ec.get('components', [])):
TypeError: 'NoneType' object is not iterable

2. An easyconfig where %(namelower)s is used in the name of a patch file of an extension, like indd-0.5.6-foss-2020a-Python-3.8.2.eb:

(see details below for traceback)

Traceback (most recent call last):
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/kehoste/work/easybuild-framework/easybuild/main.py", line 597, in <module>
    main()
  File "/Users/kehoste/work/easybuild-framework/easybuild/main.py", line 510, in main
    update_pr(options.update_pr, categorized_paths, ordered_ecs)
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1924, in update_pr
    update_branch(branch_name, paths, ecs, github_account=github_account, commit_msg=commit_msg)
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1894, in update_branch
    _, _, _, _, diff_stat, pr_target_repo = _easyconfigs_pr_common(paths, ecs, start_branch=branch_name,
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 862, in _easyconfigs_pr_common
    patch_specs = det_patch_specs(paths['patch_files'], file_info, [target_dir])
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1060, in det_patch_specs
    soft_name = find_software_name_for_patch(patch_file, ec_dirs)
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1121, in find_software_name_for_patch
    if is_patch_for(patch_name, ec['ec']):
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1027, in is_patch_for
    patches.extend(p[0] % templates if isinstance(p, (tuple, list)) else p % templates
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/github.py", line 1027, in <genexpr>
    patches.extend(p[0] % templates if isinstance(p, (tuple, list)) else p % templates
KeyError: 'namelower'

[bartoldeman]

LGTM