Fix a heap overflow in CJBig2_Context::parseSymbolDict

core/src/fxcodec/jbig2/JBig2_ArithDecoder.h

Index: core/src/fxcodec/jbig2/JBig2_ArithDecoder.h
diff --git a/core/src/fxcodec/jbig2/JBig2_ArithDecoder.h b/core/src/fxcodec/jbig2/JBig2_ArithDecoder.h
index 214688d3b2eea9670ab7f828642dc63ed8245412..33bbe39d0d34ac536b7e497ef9c99b7db708a843 100644
--- a/core/src/fxcodec/jbig2/JBig2_ArithDecoder.h
+++ b/core/src/fxcodec/jbig2/JBig2_ArithDecoder.h
@@ -72,6 +72,10 @@ inline void CJBig2_ArithDecoder::BYTEIN()
 }
 inline int CJBig2_ArithDecoder::DECODE(JBig2ArithCtx *pCX)
 {
+    if (!pCX || pCX->I >= JBIG2_QE_NUM) {
+        return 0;
+    }
+
     int D;
     const JBig2ArithQe * qe = &QeTable[pCX->I];
     A = A - qe->Qe;