#163 Crash in dami::convert if iconv_open fails

[atgraham]

iconv_close() performs a free() of the object returned
by iconv_open(). In dami::convert, the close gets
called regardless of whether or not the open succeeds,
thus causing it to attempt to free(-1). The fix is
straightforward, but here is a patch anyway.

[atgraham]

Patch to fix crash