heap-buffer-overflow in od_decode_haar_dc_sb

[tysmith]

Found running commit 4633b81

To reproduce run:
./dump_video test_case.ovg

==49255==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62900000e200 at pc 0x0000004f9cf2 bp 0x7ffc36cc0350 sp 0x7ffc36cc0348
WRITE of size 4 at 0x62900000e200 thread T0
    #0 0x4f9cf1 in od_decode_haar_dc_sb src/decode.c:644:32
    #1 0x4f9cf1 in od_decode_coefficients src/decode.c:976
    #2 0x4f9cf1 in daala_decode_packet_in src/decode.c:1204
    #3 0x4ec2de in main examples/dump_video.c:426:13
    #4 0x7f26a163d82f in __libc_start_main /build/glibc-GKVZIf/glibc-2.23/csu/../csu/libc-start.c:291
    #5 0x418f98 in _start (dump_video+0x418f98)

test_case.ovg.zip
log.txt