Fix bug in message.decryptSessionKey where it would return this (msg obj)

Cleanup message code

src/message.js

@@ -91,7 +91,10 @@ Message.prototype.getSigningKeyIds = function() {
  */
 Message.prototype.decrypt = function(privateKey) {
   var keyObj = this.decryptSessionKey(privateKey);
-  if (keyObj) {
+  if (!keyObj) {
+    // nothing to decrypt return unmodified message
+    return this;
+  }
   var symEncryptedPacketlist = this.packets.filterByTag(enums.packet.symmetricallyEncrypted, enums.packet.symEncryptedIntegrityProtected);
   if (symEncryptedPacketlist.length !== 0) {
     var symEncryptedPacket = symEncryptedPacketlist[0];
@@ -101,7 +104,6 @@ Message.prototype.decrypt = function(privateKey) {
     symEncryptedPacket.packets = new packet.List();
     return resultMsg;
   }
-  }
 };
 
 /**
@@ -126,16 +128,15 @@ Message.prototype.decryptSessionKey = function(privateKey) {
         }
       }
     }
-
     if (!keyPacket) {
       throw new Error('No symmetrically encrypted session key packet found.');
     }
-  }
-  else {
+
+  } else {
     var encryptionKeyIds = this.getEncryptionKeyIds();
     if (!encryptionKeyIds.length) {
-      // nothing to decrypt return unmodified message
-      return this;
+      // nothing to decrypt
+      return;
     }
     var privateKeyPacket = privateKey.getKeyPacket(encryptionKeyIds);
     if (!privateKeyPacket.isDecrypted) {
@@ -199,11 +200,9 @@ Message.prototype.encrypt = function(keys, passwords) {
   var symAlgo;
   if (keys) {
     symAlgo = keyModule.getPreferredSymAlgo(keys);
-  }
-  else if(passwords) {
+  } else if (passwords) {
     symAlgo = config.encryption_cipher;
-  }
-  else {
+  } else {
     throw new Error('No keys or passwords');
   }