httpcompression.patch

--- a/scrapy/contrib/downloadermiddleware/httpcompression.py
+++ b/scrapy/contrib/downloadermiddleware/httpcompression.py
@@ -33,7 +33,11 @@ class HttpCompressionMiddleware(object):
 
     def _decode(self, body, encoding):
         if encoding == 'gzip' or encoding == 'x-gzip':
-            body = gunzip(body)
+            try:
+                body = gunzip(body)
+            except IOError:
+                # leave body as is if can't decompress
+                pass
 
         if encoding == 'deflate':
             try:
@@ -44,6 +48,10 @@ class HttpCompressionMiddleware(object):
                 # http://carsten.codimi.de/gzip.yaws/
                 # http://www.port80software.com/200ok/archive/2005/10/31/868.aspx
                 # http://www.gzip.org/zlib/zlib_faq.html#faq38
-                body = zlib.decompress(body, -15)
+                try:
+                    body = zlib.decompress(body, -15)
+                except zlib.error:
+                    # leave body as is if can't decompress
+                    pass
         return body