empty content taxonomy cells imported as taxonomy terms with empty names

Issue Summary

content_taxonomy_feeds_set_target() had a bug whereby empty cells were importing as taxonomy tids with empty names. to fix, change FROM

// Return if there are no or empty terms.
if (!is_array($terms) || empty($terms)) {
return;
}

TO

// Return if there are no or empty terms.
if (!is_array($terms) || (count($terms) == 1 && empty($terms[0]))) {
return;
}

this relates to issues like:

http://drupal.org/node/1047894
http://drupal.org/node/1107522