cdx: fix the 'yield nothing' case when limit==1

add additional test case for limit==1 and reverse=True,
as limit is optimized out

pywb/cdx/cdxops.py

@@ -122,6 +122,8 @@ def cdx_reverse(cdx_iter, limit):
         for cdx in cdx_iter:
             last = cdx
 
+        if not last:
+            return
         yield last
 
     reverse_cdxs = deque(maxlen=limit)

pywb/cdx/test/cdxserver_test.py

@@ -28,6 +28,10 @@ org,iana)/_js/2013.1/jquery.js 20140126201307 https://www.iana.org/_js/2013.1/jq
 Traceback (most recent call last):
 CaptureNotFoundException: No Captures found for: http://iana.org/dont_have_this
 
+# No matching -- limit=1
+>>> cdx_ops_test('http://iana.org/dont_have_this', reverse = True, resolveRevisits = True, limit = 1)
+Traceback (most recent call last):
+CaptureNotFoundException: No Captures found for: http://iana.org/dont_have_this
 
 # Filter cdx (default: regex)
 >>> cdx_ops_test(url = 'http://iana.org/domains', matchType = 'prefix', filter = ['mimetype:text/html'])

pywb/cdx/test/test_lazy_ops.py

@@ -45,6 +45,9 @@ def test_closest():
 def test_limit():
     lazy_cdx_load(key=KEY, limit=10)
 
+def test_limit_1_reverse():
+    lazy_cdx_load(key=KEY, limit=1, reverse=True)
+
 def test_multi_ops():
     lazy_cdx_load(key=KEY,
                   resolveRevisits=True,