title: stringByAddingPercentEscapesUsingEncoding not working with NSStrings with ' 0'
body: <p>I have been having some problem with the <code>stringByAddingPercentEscapesUsingEncoding:</code> method.
  Here's what happens:</p>
  
  <p>When I try to use the method to convert the NSString:</p>
  
  <pre><code>"..City=Cl&amp;PostalCode=Rh6 0Nt"
  </code></pre>
  
  <p>I get this this..</p>
  
  <pre><code>"City=Cl&amp;PostalCode=Rh62t"
  </code></pre>
  
  <p>It should be:</p>
  
  <pre><code>"..City=Cl&amp;PostalCode=Rh6%200Nt"
  </code></pre>
  
  <p>What can I do about this? Thanks in advance !!</p>