[XERCESC-2180] Remove assertion when a surrogate pair is split by the boundary
of an input buffer (transcoders try to avoid this, but UTF-16 transcoder doesn't
have this check in place). The reader now pulls in more data on demand.

git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@1871620 13f79535-47bb-0310-9956-ffa450edef68
4 files changed