Changeset [6147eb07bf00770bd5bb09ae905342f0117ff502] by Christophe Fergeau

make sure 'length' is >=0 in afc_file_read

trying to read a negative amount of data doesn't make much sense, and the
returned 'bytes' value will overflow if we try to do that. Just treat
negative length values as an invalid argument. An alternative way of
handling it would be to silently return OK/0 bytes read.
http://github.com/MattColyer/libiphone/commit/6147eb07bf00770bd5bb0...