#170 convert_i gets stuck in an infinite loop

[atgraham]

{anonymous}::convert_i(iconv_t cd, String source) in
utils.cpp

This function gets stuck in an infinite loop on some
invalid data inputs. For instance, if you attempt to
convert a UTF-16 string that is an odd length, it will
get stuck in the "do" loop because iconv will always
return -1 with errno EINVAL.

In some cases (though perhaps not all), EINVAL should
cause the loop to exit.