Fix segfault in init context.

Fix segfault in init context.

The init context function was improperly initializing the ctx variable (too
late) when some early error conditions can happen. Therefore passing to the
delete context function a random memory address it would then try to free.
This wuld cause a SEGFAULT in most cases.

Additionally unfortunately iconv_close() does not follow good practices and
blindignly dereferences data, even if the passed in pointer is NULL.
So add a check before calling.