refactor: add function annotation and check return value

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>

rename_regions_from_markers.lua

@@ -9,7 +9,9 @@ ardour {
 function factory()
     -- there is currently no direct way to find the track
     -- corresponding to a [selected] region
-    function find_track_for_region(region_id)
+    ---@param region_id ID
+    ---@return Track?
+    local function find_track_for_region(region_id)
         for route in Session:get_tracks():iter() do
             local track = route:to_track()
             local pl = track:playlist()
@@ -20,7 +22,7 @@ function factory()
         assert(0)  -- can't happen, region must be in a playlist
     end
 
-    return function()
+    return function ()
         local sel = Editor:get_selection()  -- get current selection
         local loc = Session:locations()     -- get locations
 
@@ -30,8 +32,7 @@ function factory()
         -- for each selected region...
         for region in sel.regions:regionlist():iter() do
             -- test if it's an audio region
-            local ar = region:to_audioregion()
+            if region:to_audioregion():isnil() then
-            if ar:isnil() then
                 goto next
             end
 
@@ -48,6 +49,7 @@ function factory()
 
             local track = find_track_for_region(rid)
 
+            if track then
                 region:to_stateful():clear_changes()
 
                 --~ print("Marker label:", mloc:name())
@@ -56,6 +58,7 @@ function factory()
 
                 -- collect undo data
                 Session:add_stateful_diff_command(region:to_statefuldestructible())
+            end
 
             ::next::
         end