shutil.copytree incorrectly does not copy symlink contents if called
with symlink=False and ignore_dangling_symlinks=True.

The wrong behaviour can be reproduced like this:

$ tree
.
└── a
    ├── a.txt
    └── b
        └── a.txt -> ../a.txt

$ python3 -c "import shutil;shutil.copytree('a/b', 'c', symlinks=False, ignore_dangling_symlinks=True)"

As a result directoy c will be created but it will remain empty.
Expected result is a file c/a.txt with the contents of a/b/a.txt.