OSV-2018-310 Use-of-uninitialized-value in jbig2_arith_decode

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5636 Crash type: Use-of-uninitialized-value Crash state: jbig2arithdecode jbig2decodegenerictemplate0unopt jbig2decodegenericregion...