hgweb: fix handling of arguments in the between command

The 'pairs' argument was coded to be optional, but the code would
crash if it was not provided.

mercurial/hgweb/protocol.py

@@ -62,9 +62,8 b' def branches(repo, req):'
     yield resp
 
 def between(repo, req):
-    if 'pairs' in req.form:
-        pairs = [map(bin, p.split("-"))
-                 for p in req.form['pairs'][0].split(" ")]
+    pairs = [map(bin, p.split("-"))
+             for p in req.form['pairs'][0].split(" ")]
     resp = cStringIO.StringIO()
     for b in repo.between(pairs):
         resp.write(" ".join(map(hex, b)) + "\n")