imp:web: show zero amounts with their commodity symbol(s?) [#2140]

This was mainly to make the sidebar more informative,
but also affects and hopefully helps, all amounts displayed elsewhere.

hledger-web/Hledger/Web/Widget/Common.hs

@@ -95,7 +95,7 @@ accountOnlyQuery = ("inacctonly:" <>) . quoteIfSpaced
 
 mixedAmountAsHtml :: MixedAmount -> HtmlUrl a
 mixedAmountAsHtml b _ =
-  for_ (lines (showMixedAmountWithoutCost False b)) $ \t -> do
+  for_ (lines (showMixedAmountWith noCostFmt{displayZeroCommodity=True} b)) $ \t -> do
     H.span ! A.class_ c $ toHtml t
     H.br
   where