Initialize bigint

src/preserves.nim

@@ -188,7 +188,7 @@ proc concat(result: var string; prs: Preserve) =
   of pkByteString:
     for b in prs.bytes:
       if b.char notin {'\20'..'\21', '#'..'[', ']'..'~'}:
-        result.add("#[")
+        result.add("#[") #]#
         result.add(base64.encode(prs.bytes))
         result.add(']')
         return
@@ -459,7 +459,7 @@ proc decodePreserves*(s: Stream): Preserve =
     discard s.readUint8()
   of 0xb0:
     let len = s.readVarint()
-    result = Preserve(kind: pkBigInteger)
+    result = Preserve(kind: pkBigInteger, bigint: initBigint 0)
     for _ in 1..len:
       result.bigint = (result.bigint shl 8) + s.readUint8().int32
   else: