hgweb: fix type of {nav} keyword when linerange filter is active

Spotted by making '%' operator check the operand type more strictly. Before,
"{nav}" would be evaluated to a lazy "" (empty string) and {"" % x} would
yield one empty string.

mercurial/hgweb/webcommands.py

@@ -1082,7 +1082,7 b' def filelog(web):'
         linerange = webutil.formatlinerange(*lrange)
         # deactivate numeric nav links when linerange is specified as this
         # would required a dedicated "revnav" class
-        nav = None
+        nav = []
         if descend:
             it = dagop.blockdescendants(fctx, *lrange)
         else: