hgweb: enumerate lines in loop header, not before

Doing this will allow access to the lines in arbitrary order (because the
result of enumerate() is an iterator), and that will help calculating rowspan
for annotate blocks.

mercurial/hgweb/webcommands.py

@@ -875,13 +875,12 b' def annotate(web, req, tmpl):'
         if util.binary(fctx.data()):
             mt = (mimetypes.guess_type(fctx.path())[0]
                   or 'application/octet-stream')
-            lines = enumerate([((fctx.filectx(fctx.filerev()), 1),
-                                '(binary:%s)' % mt)])
+            lines = [((fctx.filectx(fctx.filerev()), 1), '(binary:%s)' % mt)]
         else:
-            lines = enumerate(fctx.annotate(follow=True, linenumber=True,
-                                            diffopts=diffopts))
+            lines = fctx.annotate(follow=True, linenumber=True,
+                                  diffopts=diffopts)
         previousrev = None
-        for lineno, ((f, targetline), l) in lines:
+        for lineno, ((f, targetline), l) in enumerate(lines):
             rev = f.rev()
             blockhead = rev != previousrev or None
             previousrev = rev