Fix peer communication vulnerability (no known exploits) reported by Ben Hawkes

git-svn-id: file:///data/workdir/Transmission-svn//trunk@14303 1bcf1a7e-6170-4b50-b784-84ec52b2dec6
fix tr_bencParseStr() bug reported by Ben Hawkes

git-svn-id: file:///data/workdir/Transmission-svn//trunk@14304 1bcf1a7e-6170-4b50-b784-84ec52b2dec6