querystring: manage percent character at unescape

Related: #33892
Fixes: #35012

PR-URL: #35013
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/querystring.js

@@ -94,13 +94,13 @@ function unescapeBuffer(s, decodeSpaces) {
       hexHigh = unhexTable[currentChar];
       if (!(hexHigh >= 0)) {
         out[outIndex++] = 37; // '%'
+        continue;
       } else {
         nextChar = s.charCodeAt(++index);
         hexLow = unhexTable[nextChar];
         if (!(hexLow >= 0)) {
           out[outIndex++] = 37; // '%'
-          out[outIndex++] = currentChar;
-          currentChar = nextChar;
+          index--;
         } else {
           hasHex = true;
           currentChar = hexHigh * 16 + hexLow;

test/parallel/test-querystring.js

@@ -175,7 +175,10 @@ const qsUnescapeTestCases = [
   ['there%2Qare%0-fake%escaped values in%%%%this%9Hstring',
    'there%2Qare%0-fake%escaped values in%%%%this%9Hstring'],
   ['%20%21%22%23%24%25%26%27%28%29%2A%2B%2C%2D%2E%2F%30%31%32%33%34%35%36%37',
-   ' !"#$%&\'()*+,-./01234567']
+   ' !"#$%&\'()*+,-./01234567'],
+  ['%%2a', '%*'],
+  ['%2sf%2a', '%2sf*'],
+  ['%2%2af%2a', '%2*f*']
 ];
 
 assert.strictEqual(qs.parse('id=918854443121279438895193').id,