title: Cannot use utf-8 encoded image filename in order to customize node shape
body: <p>I've saved DOT code file in utf-8 encoding. But it cannot output png image file with customized shape. Is there an example to demonstrate user specified charset usage of graphviz? </p>
  
  <p>The demo code is here.</p>
  
  <pre><code>digraph G {
  
      bgcolor=black;
      edge [arrowsize=1, color=red];
  
      node [penwidth=1, color=white, labelloc=b];
  
      BR [shape=box, label="BR", charset="utf-8", image="图元.png"];
      DS [shape=plaintext, fontname="SimSun", fontcolor=white, fontsize=18, label="测点"];
      BR -&gt; DS[dir=forward];
  }
  </code></pre>
  
  <p>And the results of command-line are listed as following.</p>
  
  <pre><code>C:\dot&gt;dot -Gcharset=utf-8 -Tpng -o demo.png demo.dot
  Warning: No such file or directory while opening 鍥惧厓.png
  Warning: No or improper image="鍥惧厓.png" for node "BR"
  </code></pre>