metadata_iterators.c : Set status when metadata itereator is not writable.
metadata_iterators.c : Set status when metadata itereator is not writable.

The status should be FLAC__METADATA_SIMPLE_ITERATOR_STATUS_ILLEGAL_INPUT.

Closes: http://sourceforge.net/p/flac/patches/50/

waitman/flac,waitman/flac,waitman/flac,waitman/flac,waitman/flac