heap-buffer-overflow in od_img_plane_edge_ext

[tysmith]

Found running commit 4633b81
Built with AddressSanitizer

To reproduce run:
./dump_video test_case.ogv

==47159==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7f957fb3d820 at pc 0x00000055daa7 bp 0x7ffc2135f9b0 sp 0x7ffc2135f9a8
READ of size 16 at 0x7f957fb3d820 thread T0
    #0 0x55daa6 in od_img_plane_edge_ext src/state.c:1086:28
    #1 0x55daa6 in od_img_edge_ext src/state.c:1107
    #2 0x4f907f in daala_decode_packet_in src/decode.c:1219:3
    #3 0x4ec2de in main examples/dump_video.c:426:13
    #4 0x7f957e87682f 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.ogv.zip