Core/Common: fix a bug in BigNumber::AsByteArray that was causing incorrect output in 1/256 cases with explicit minSize (iff MSB zero)

(cherry picked from commit b2b9880377f75a333b94a71ce6076016b8285e0b)

src/common/Cryptography/BigNumber.cpp

@@ -183,11 +183,11 @@ std::unique_ptr<uint8[]> BigNumber::AsByteArray(int32 minSize, bool littleEndian
     if (length > numBytes)
         memset((void*)array, 0, length);
 
-    BN_bn2bin(_bn, (unsigned char *)array);
+    BN_bn2bin(_bn, array + (length-numBytes));
 
     // openssl's BN stores data internally in big endian format, reverse if little endian desired
     if (littleEndian)
-        std::reverse(array, array + numBytes);
+        std::reverse(array, array + length);
 
     std::unique_ptr<uint8[]> ret(array);
     return ret;