Support PKCS5 padding longer than 8 bytes (#1081)

This is allowed by the spec to hide the length of the session key:

    For example, assuming that an AES algorithm is
    used for the session key, the sender MAY use 21, 13, and 5 bytes of
    padding for AES-128, AES-192, and AES-256, respectively, to provide
    the same number of octets, 40 total, as an input to the key wrapping
    method.

src/crypto/pkcs5.js

@@ -41,7 +41,7 @@ function decode(msg) {
   const len = msg.length;
   if (len > 0) {
     const c = msg.charCodeAt(len - 1);
-    if (c >= 1 && c <= 8) {
+    if (c >= 1) {
       const provided = msg.substr(len - c);
       const computed = String.fromCharCode(c).repeat(c);
       if (provided === computed) {