Corrects scenario where no src_dir is set -5.x

[cerrussell]

Trying to get the src_dir from the bom path is good, but we need to still set src_dir to the current working directory if depscan hasn't been run using the --bom argument (or when the bom does not actually exist). Otherwise, we will run into problems as we later assume src_dir has been set and try to use it, which will result in an exception.

    if not src_dir or src_dir == ".":
        if src_dir == "." or args.search_purl:
            src_dir = os.getcwd()
        # Try to infer from the bom file
        elif args.bom and os.path.exists(args.bom):
            src_dir = os.path.dirname(os.path.realpath(args.bom))

This PR corrects the problem.

[prabhu]

@cerrussell, please rebase from release/5.x to get the CI fixes