fix: Avoid raising exception for invalid path problems

When the feed was not declared as iTunes and the summary method was
trieggered an Nokogiri error was raised, because the summary had an
undeclared namespace. We now avoid that and return nil.

lib/house/episode.rb

@@ -70,6 +70,8 @@ def item_attr(xpath, attribute = nil)
           node.attr(attribute).value
         end
       end
+    rescue Nokogiri::XML::XPath::SyntaxError => e
+      nil
     end
   end
 end

lib/house/podcast.rb

@@ -75,6 +75,8 @@ def attr(xpath)
       else
         node.text
       end
+    rescue Nokogiri::XML::XPath::SyntaxError => e
+      nil
     end
   end
 end

spec/lib/house/podcast_spec.rb

@@ -86,6 +86,7 @@
         podcast = House::Podcast.new("http://podcasts.example.com/valid_with_items_without_itunes.xml")
         item = podcast.items.first
         item.subtitle.should be_nil
+        item.summary.should be_nil
         item.keywords.should be_empty
         item.duration.should be_nil
       end

spec/test_data/valid_with_2_items.xml

@@ -3,23 +3,23 @@
   <channel>
     <title>Example Podcast</title>
     <itunes:author>Example Author</itunes:author>
-    <link>http://podcasts.example.com</link> 
+    <link>http://podcasts.example.com</link>
     <itunes:explicit>no</itunes:explicit>
     <itunes:subtitle>iTunes Example Subtitle</itunes:subtitle>
     <itunes:owner>
-    	<itunes:name>iTunes Example Owner</itunes:name>
-    	<itunes:email>[email protected]</itunes:email>
+      <itunes:name>iTunes Example Owner</itunes:name>
+      <itunes:email>[email protected]</itunes:email>
     </itunes:owner>
     <image>
-    	<url>http://podcasts.example.com/example2.jpg</url>
-    	<title>Example Podcast</title>
-    	<link>http://www.example.com</link>
+      <url>http://podcasts.example.com/example2.jpg</url>
+      <title>Example Podcast</title>
+      <link>http://www.example.com</link>
     </image>
     <itunes:link rel="image" type="video/jpeg" href="http://www.example.com/example.jpg">Example Podcast</itunes:link>
     <itunes:category text="Music" />
     <itunes:summary>iTunes Example Summary</itunes:summary>
-    <description>Can't get enough of the radioshow Tiësto's Club Life? Then subscribe to this podcast and get a weekly update on the favourite tracks of Tiësto! For more info about Tiësto please visit www.tiesto.com or club.bnn.nl</description> 
-    <language>EN</language> 
+    <description>Can't get enough of the radioshow Tiësto's Club Life? Then subscribe to this podcast and get a weekly update on the favourite tracks of Tiësto! For more info about Tiësto please visit www.tiesto.com or club.bnn.nl</description>
+    <language>EN</language>
     <webmaster>[email protected]</webmaster> 
     <lastBuildDate>Mon, 28 May 2012 13:00:00 GMT</lastBuildDate>                 
     <atom10:link xmlns:atom10="http://www.w3.org/2005/Atom" rel="self" type="application/rss+xml" href="http://feeds.feedburner.com/example" />
@@ -37,13 +37,14 @@
 
       <itunes:link rel="image" type="video/jpeg" href="http://podcasts.example.com/example2.jpg">Podcast 2 Example Image</itunes:link>
       <enclosure url="http://podcasts.example.com/example2.m4a" length="0" type="audio/mpeg" />
-    <feedburner:origEnclosureLink>http://tracks.example.com/example2.m4a</feedburner:origEnclosureLink>
+      <feedburner:origEnclosureLink>http://tracks.example.com/example2.m4a</feedburner:origEnclosureLink>
     </item>
     <item>
       <pubDate>Mon, 23 March 1999 23:00:00 GMT</pubDate>
       <title>Example Podcast 1</title>
       <author>Example Author 1</author>
       <itunes:author>Example Author 1</itunes:author>
+      <itunes:summary>iTunes Example Summary</itunes:summary>
       <itunes:subtitle>Example Subtitle 1</itunes:subtitle>
       <itunes:keywords>dance,david,electronica,guetta,house,podcast,radio,video</itunes:keywords>
       <itunes:duration>1:01:11</itunes:duration>

spec/test_data/valid_without_itunes.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<rss xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd" xmlns:feedburner="http://rssnamespace.org/feedburner/ext/1.0" version="2.0">
+<rss version="2.0" xmlns:content="http://purl.org/rss/1.0/modules/content/" xmlns:wfw="http://wellformedweb.org/CommentAPI/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:sy="http://purl.org/rss/1.0/modules/syndication/" xmlns:slash="http://purl.org/rss/1.0/modules/slash/">
   <channel>
     <title>Example Podcast</title>
     <link>http://podcasts.example.com</link>