filter-utils: fix handling of targetless smart filters

A smart filter should be considered "targetless" (i.e. interpose on
streams going to default target) only if filter.smart.target is not set.

Currently any smart filter with specified target not found is considered
such, which is wrong.  This causes misbehavior, such as all recording
streams going to the bluetooth dummy source.

Fix this by doing it correctly.

src/scripts/lib/filter-utils.lua

@@ -157,6 +157,19 @@ local function getFilterSmartTarget (metadata, node, om)
   return target
 end
 
+local function getFilterSmartTargetless (metadata, node)
+  local id = node["bound-id"]
+  local value_str = nil
+  if metadata ~= nil then
+    value_str = metadata:find (id, "filter.smart.target")
+  end
+  if value_str == nil then
+    value_str = node.properties ["filter.smart.target"]
+  end
+
+  return value_str == nil
+end
+
 local function getFilterSmartBefore (metadata, node)
   -- Check metadata and fallback to properties
   local id = node["bound-id"]
@@ -312,6 +325,7 @@ local function rescanFilters (om, metadata_om)
     filter.disabled = getFilterSmartDisabled (metadata, n)
     filter.targetable = getFilterSmartTargetable (metadata, n)
     filter.target = getFilterSmartTarget (metadata, n, om)
+    filter.targetless = getFilterSmartTargetless (metadata, n)
     filter.before = getFilterSmartBefore (metadata, n)
     filter.after = getFilterSmartAfter (metadata, n)
 
@@ -471,7 +485,7 @@ function module.get_filter_from_target (direction, si_target)
         not v.disabled and
         v.smart and
         ((v.target ~= nil and target ~= nil and v.target.id == target.id) or
-            (target == nil and v.target == nil)) then
+            (target == nil and v.targetless)) then
       return v.main_si
     end
   end