Fix attrib check code for library_content import
Attributes come in as a list of dicts with strings as keys and values.
Implicitly casting each result as a tuple causes the code to split the key string into it's characters.
This yields a list of characters, the first two of which are placed into the variables "attr_name" and "attr_value".
This is not only wrong, but because keys tend to be more than 2 characters, the net result is:
`ValueError: too many values to unpack`