Break out of FRU read if zero data returned

If a BMC returns 0 data, then assume end of data has been
reached.  Not all implementations accurately advertise FRU
size, so this is a way to detect and break out.

Change-Id: I03d0393563f8527e16830098b649ae940ee7ee9e

pyghmi/ipmi/fru.py

@@ -172,6 +172,8 @@ class FRU(object):
                 raise iexc.IpmiException(response['error'], response['code'])
             self.rawfru.extend(response['data'][1:])
             offset += response['data'][0]
+            if response['data'][0] == 0:
+                break
             if offset + chunksize > frusize:
                 chunksize = frusize - offset