A short, malformed input to bzip2 decompressor may crash the process.

Reproducer: http://play.golang.org/p/l_7Aaj6UAI

go1.3
panic: runtime error: index out of range [recovered]
    panic: runtime error: index out of range

goroutine 16 [running]:
runtime.panic(0x128a60, 0x1bce9c)
    /tmp/sandbox/go/src/pkg/runtime/panic.c:279 +0x120
io/ioutil.func·002()
    /tmp/sandbox/go/src/pkg/io/ioutil/ioutil.go:30 +0x140
runtime.panic(0x128a60, 0x1bce9c)
    /tmp/sandbox/go/src/pkg/runtime/panic.c:248 +0x1e0
compress/bzip2.(*reader).readBlock(0x10410d80, 0x30, 0x0, 0x0)
    /tmp/sandbox/go/src/pkg/compress/bzip2/bzip2.go:353 +0x10c0
compress/bzip2.(*reader).read(0x10410d80, 0x10452000, 0x200, 0x200, 0x104280b8, 0x0,
0x0, 0x10452000)
    /tmp/sandbox/go/src/pkg/compress/bzip2/bzip2.go:184 +0x720
compress/bzip2.(*reader).Read(0x10410d80, 0x10452000, 0x200, 0x200, 0x129a00, 0x0, 0x0,
0x1)
    /tmp/sandbox/go/src/pkg/compress/bzip2/bzip2.go:101 +0x140
bytes.(*Buffer).ReadFrom(0x10426240, 0xfefd0280, 0x10410d80, 0x0, 0x0, 0x0, 0x0, 0x0)
    /tmp/sandbox/go/src/pkg/bytes/buffer.go:169 +0x260
io/ioutil.readAll(0xfefd0280, 0x10410d80, 0x200, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
    /tmp/sandbox/go/src/pkg/io/ioutil/ioutil.go:33 +0x200
io/ioutil.ReadAll(0xfefd0280, 0x10410d80, 0x0, 0x0, 0x0, 0x0, 0x0, 0x1040e130)
    /tmp/sandbox/go/src/pkg/io/ioutil/ioutil.go:42 +0x80
main.main()
    /tmpfs/gosandbox-6c2ae51f_78c3bfb7_2829f08e_ee1280e1_97e122b2/prog.go:19 +0x240