libexif has numerous cases where errors are not propagated

Many functions in libexif have no means at all for
returning an error code.

Those functions usually return void and the calling
function has no way to find out whether the called
function succeeded or failed.

Examples are:
<ul>
<li>
exif_loader_get_data() calling exif_data_log() and
exif_data_load_data() (<a
href="https://sourceforge.net/tracker/index.php?func=detail&amp;aid=1169170&amp;group_id=12272&amp;atid=112272">#1169170</a>
</li>
<li>
exif_data_load_data() calling exif_mnote_data_canon_load()
(<a
href="https://sourceforge.net/tracker/index.php?func=detail&amp;aid=1054323&amp;group_id=12272&amp;atid=112272">#1054323</a>
</li>
</ul>

The full extent of the problem and whether fixing it
requires changing the ABI or API still has to be
determined.