title: Knitting returns parse error
body: <p>In attempting to knit a PDF. I'm calling a script that should return two ggplots by calling the chunk:</p>
  
  <pre><code>```{r, echo=FALSE}
  
  read_chunk('Script.R')
  
  ```r
  </code></pre>
  
  <p>But receive the error</p>
  
  <pre><code>processing file: Preview-24a46368403c.Rmd
  
   Quitting from lines 9-12 (Preview-24a46368403c.Rmd)  Error in
   parse(text = x, srcfile = src) :    attempt to use zero-length
   variable name Calls: &lt;Anonymous&gt; ... &lt;Anonymous&gt; -&gt; parse_all -&gt;
   parse_all.character -&gt; parse Execution halted
  </code></pre>
  
  <p>The script on its own runs and returns the two plots, but won't return them when knitted. </p>
  
  <p>Similarly attempted to use <code>source()</code>
  But got a similar error </p>
  
  <pre><code> Quitting from lines 7-10 (Preview-24a459ca4c1.Rmd)  Error in
   file(filename, "r", encoding = encoding) :    cannot open the
   connection Calls: &lt;Anonymous&gt; ... withCallingHandlers -&gt; withVisible
   -&gt; eval -&gt; eval -&gt; source -&gt; file Execution halted
  </code></pre>