fix comments containing tilde

Author: smhg

lib/poparser.js

@@ -174,7 +174,7 @@ Parser.prototype._lexer = function (chunk) {
       case this.states.comments:
         if (chr === '\n') {
           this._state = this.states.none;
-        } else if (chr === '~') {
+        } else if (chr === '~' && this._node.value === '') {
           this._node.value += chr;
           this._state = this.states.obsolete;
         } else if (chr !== '\r') {