msgfmt: Fix a buffer overrun.
Reported by Tobi Schäfer at <https://trac.macports.org/ticket/58323>,
via Ryan Schmidt <@ryandesign.com> at <https://savannah.gnu.org/bugs/?56112>.
Patch proposed by Joshua Root.
* gettext-tools/src/write-java.c (msgid_hashcode): Allocate memory for the
trailing NUL byte as well.
