oss-fuzz: MemorySanitizer: use-of-uninitialized-value in loop_filter_h_sb128uv_c
reproduce with ./tests/dav1d_fuzzer clusterfuzz-testcase-minimized-dav1d_fuzzer-5693881400688640
clusterfuzz-testcase-minimized-dav1d_fuzzer-5693881400688640
==909==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x7f3b54a71d1a in loop_filter_h_sb128uv_c (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x18dd1a)
#1 0x7f3b54a6ffc9 in dav1d_loopfilter_sbrow_16bpc (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x18bfc9)
#2 0x7f3b54ab307f in dav1d_filter_sbrow_16bpc (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x1cf07f)
#3 0x7f3b549603db in dav1d_decode_frame (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x7c3db)
#4 0x7f3b54966007 in dav1d_submit_frame (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x82007)
#5 0x7f3b54943422 in dav1d_parse_obus (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x5f422)
#6 0x7f3b54ab7abe in dav1d_decode (/home/janne/src/dav1d/build-msan-fuzz/tests/../src/libdav1d.so.0+0x1d3abe)
#7 0x4c67df in LLVMFuzzerTestOneInput (/home/janne/src/dav1d/build-msan-fuzz/tests/dav1d_fuzzer+0x4c67df)
#8 0x42e062 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /var/tmp/portage/sys-libs/compiler-rt-sanitizers-7.0.0/work/compiler-rt-7.0.0.src/lib/fuzzer/FuzzerLoop.cpp:576:15
#9 0x41fbad in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) /var/tmp/portage/sys-libs/compiler-rt-sanitizers-7.0.0/work/compiler-rt-7.0.0.src/lib/fuzzer/FuzzerDriver.cpp:280:6
#10 0x424782 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) /var/tmp/portage/sys-libs/compiler-rt-sanitizers-7.0.0/work/compiler-rt-7.0.0.src/lib/fuzzer/FuzzerDriver.cpp:714:9
#11 0x44d642 in main /var/tmp/portage/sys-libs/compiler-rt-sanitizers-7.0.0/work/compiler-rt-7.0.0.src/lib/fuzzer/FuzzerMain.cpp:20:10
#12 0x7f3b53970ae6 in __libc_start_main (/lib64/libc.so.6+0x21ae6)
#13 0x41df69 in _start (/home/janne/src/dav1d/build-msan-fuzz/tests/dav1d_fuzzer+0x41df69)