csn1_dec.c: Fix stored bit in CSN_NEXT_EXIST_LH

Fixup for previous patch, which forgot to update the pui using the new
variable, as done already in the same patch for M_NEXT_EXIST.

Change-Id: I92a04c708bcc6c15348324321e8890361bbc5c31
Fixes: 72cdb30ee2b1c0d71ff6d9583d51f46b2e5fdcea

src/csn1_dec.c

@@ -996,7 +996,7 @@ csnStreamDecoder(csnStream_t* ar, const CSN_DESCR* pDescr, struct bitvec *vector
           }
         }
         LOGPC(DCSN1, LOGL_DEBUG, "%s = %u%s | ", pDescr->sz , (unsigned)fExist, fExist && isnull ? " (NULL)" : "");
-        *pui8++   = fExist;
+        *pui8++   = !isnull;
         remaining_bits_len -= 1;
 
         bit_offset++;