[dep-quant] Fix read out of bounds

Author: Jovasa

Diff for: src/dep_quant.c

@@ -573,8 +573,8 @@ static INLINE void update_common_context(
   uint8_t*       sbbFlags = cc->m_allSbbCtx[cc->m_curr_sbb_ctx_offset].sbbFlags;
   uint8_t*       levels = cc->m_allSbbCtx[cc->m_curr_sbb_ctx_offset].levels;
   size_t         setCpSize = cc->m_nbInfo[scan_pos - 1].maxDist * sizeof(uint8_t);
-  int8_t         prev_sbb_state = ctxs->m_allStates.m_refSbbCtxId[prev_state];
-  if (prev_state != -1 && prev_sbb_state >= 0) {
+  if (prev_state != -1) {
+    const int8_t prev_sbb_state = ctxs->m_allStates.m_refSbbCtxId[prev_state];
     for (int i = 0; i < numSbb; ++i) {
       sbbFlags[i * 4 + curr_state_without_offset] = cc->m_allSbbCtx[cc->m_prev_sbb_ctx_offset].sbbFlags[i * 4 + prev_sbb_state];
     }