fix multiple header fetch parsing

lib/imap.parsers.js

@@ -104,9 +104,12 @@ exports.parseFetchBodies = function(str, literals) {
         else if (typeof 
         result[i][0] += '>';
       }*/ else if (result[i].length > 1) {
-        // HEADER.FIELDS (foo)
+        // HEADER.FIELDS (foo) or HEADER.FIELDS (foo bar baz)
         result[i][0] += ' (';
-        result[i][0] += result[i].slice(1).join(' ');
+        if (Array.isArray(result[i][1]))
+          result[i][0] += result[i][1].join(' ');
+        else
+          result[i][0] += result[i].slice(1).join(' ');
         result[i][0] += ')';
       }
       if (bodies === undefined)