title: r wordcloud external ttf vfont not recognized
body: <p>I've installed the 'extrafont' package in order to install an external font library <a href="http://www.allfreefonts.com/font-4170-duality.html" rel="noreferrer">Duality</a> via the ttf_import() method. However, when specifying the font via the wordcloud method, I receive the following error:</p>
  
  <p>Installation command:</p>
  
  <pre><code># Assuming the font file, DUALITY_.ttf, is in the working directory (see link to font above)
  font_import(".",FALSE,pattern="DUALITY")
  </code></pre>
  
  <p>Wordcloud command:</p>
  
  <pre><code>wordcloud(ap.d$word, ap.d$freq, scale=c(8,2), min.freq=10, vfont=c("Duality","plain"),
        random.order=FALSE, rot.per=0, use.r.layout=FALSE, colors=pal2, fixed.asp=FALSE)
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>Error in strwidth(words[i], cex = size[i], ...) : 
    invalid 'vfont' value [typeface -2147483648]
  </code></pre>
  
  <p>In order to verify that the font is indeed installed, I issued the following commands</p>
  
  <pre><code>&gt; choose_font("Duality")
  [1] "Duality"
  &gt; fonts()
  ....[49] "Waree"                    "Duality"    
  </code></pre>
  
  <p>How come the Duality font is not visible to the vfont parameter of wordcloud? And how do I make it visible to Cairo (the default renderer). TIA!</p>