fix blank filename (#149)

Author: NamelessAssassin

utils/filename_factory.lua

@@ -50,9 +50,18 @@ end)()
 local make_media_filename = function()
     filename = mp.get_property("filename") -- filename without path
     filename = h.remove_extension(filename)
-    filename = h.remove_filename_text_in_parentheses(filename)
-    filename = h.remove_text_in_brackets(filename)
-    filename = h.remove_special_characters(filename)
+
+    local operations = {
+        h.remove_filename_text_in_parentheses, 
+        h.remove_text_in_brackets, 
+        h.remove_special_characters
+    }
+    for _, f in ipairs(operations) do
+        local temp_filename = f(filename)
+        if temp_filename ~= "" then
+            filename = temp_filename
+        end
+    end
 end
 
 local function timestamp_range(start_timestamp, end_timestamp, extension)