Errors when selecting file using "Keep" importer in FileSystem dock

[akien-mga]

Godot version:
cd05653, after #47268.

OS/device including version:
Linux, but should happen on any OS.

Issue description:
When using the new "Keep" import mode for a given file (here CSV), the following errors can be reproduced:

1. When you select the file in the FileSystem dock with a single mouse click, this error is printed:

ERROR: Couldn't find the given section "remap" and key "type", and no default was given.
   at: get_value (core/io/config_file.cpp:85)

2. When you double-click the file, or "open" it with ui_accept, the following errors are raised:

ERROR: Resource file not found: .
   at: _load (core/io/resource_loader.cpp:207)
ERROR: Failed loading resource: res://test.csv. Make sure resources have been imported by opening the project in the editor at least once.
   at: _load (core/io/resource_loader.cpp:202)
ERROR: Condition "!res.is_valid()" is true. Returning: ERR_CANT_OPEN
   at: load_resource (editor/editor_node.cpp:1016)

3. The CSV is shown with a "broken import" icon. It should likely use a "plain file" icon instead.

Steps to reproduce:
See above.

Minimal reproduction project:
CSVImporterKeep.zip