Check for zero 'sz' in dav1d_init_get_bits()

If a zero 'sz' is passed to dav1d_init_get_bits(), set c->eof to true.
Alternatively we could assert that 'sz' is nonzero.
33 jobs for patch-4 in 14 minutes and 34 seconds (queued for 32 seconds)
latest
Status Job ID Name Coverage
  Style
passed #409697
amd64 docker
style-check

00:00:28

 
  Build
passed #409708
amd64 docker
build-android-aarch64

00:00:20

passed #409707
amd64 docker
build-android-armv7

00:00:23

passed #409698
amd64 avx2 docker
build-debian

00:01:00

passed #409709
aarch64 docker
build-debian-aarch64

00:01:13

passed #409710
aarch64 docker
build-debian-aarch64-clang-5

00:00:53

passed #409713
armv7 docker
build-debian-armv7

00:00:42

passed #409714
armv7 docker
build-debian-armv7-clang-5

00:00:34

passed #409701
amd64 docker
build-debian-examples

00:00:41

passed #409716
ppc64le docker
build-debian-ppc64le

00:01:43

passed #409699
amd64 docker
build-debian-static

00:00:37

passed #409712
aarch64 docker
build-debian-werror

00:00:30

passed #409700
amd64 docker
build-debian32

00:00:53

passed #409711
macos
build-macos

00:00:32

passed #409717
amd64 docker
build-pages

00:00:17

passed #409715
amd64 docker
build-ubuntu-snap

00:00:28

passed #409705
amd64 docker
build-win-arm32

00:00:22

passed #409706
amd64 docker
build-win-arm64

00:00:22

passed #409702
amd64 docker
build-win32

00:00:51

passed #409703
amd64 docker
build-win32-unaligned-stack

00:00:34

passed #409704
amd64 docker
build-win64

00:00:51

 
  Test
passed #409718
amd64 docker
test-debian

00:00:49

98.1985%
passed #409727
aarch64 docker
test-debian-aarch64

00:02:14

passed #409729
armv7 docker
test-debian-armv7-clang-5

00:00:49

passed #409723
amd64 docker
test-debian-asan

00:01:25

passed #409719
avx2 amd64 docker
test-debian-asm

00:01:02

passed #409724
amd64 docker
test-debian-msan

00:00:54

passed #409721
amd64 docker
test-debian-mt

00:00:52

passed #409728
ppc64le docker
test-debian-ppc64le

00:02:06

passed #409725
amd64 docker
test-debian-ubsan

00:01:09

passed #409722
amd64 avx2 docker
test-debian-unaligned-stack

00:00:45

passed #409720
avx2 amd64 docker
test-debian32-asm

00:00:59

passed #409726
amd64 avx2 docker
test-win64

00:01:10