Error handling a request with multiple Surrogate-Capability headers

[asharpe-squiz]

The error manifests as

state_machine.lua:44: state 'fetching' failed to call action 'fetch': ledge/lib/ledge/handler.lua:448: attempt to concatenate local 'sc' (a table value), client: ...

and this might be a reasonable workaround...

diff --git lib/ledge/handler.lua lib/ledge/handler.lua
index f65fd7c5..9817666e 100644
--- lib/ledge/handler.lua
+++ lib/ledge/handler.lua
@@ -445,6 +445,7 @@ local function fetch_from_origin(self)
         if not sc then
             headers["Surrogate-Capability"] = capability_entry
         else
+            if type(sc) == "table" then sc = tbl_concat(sc, ", ") end
             headers["Surrogate-Capability"] = sc .. ", " .. capability_entry
         end
     end

Alternatively we could turn a string into a table and append