Merge #6285

6285: Clear editor file browser search term when entering folder r=Chairn a=Robyt3

Closes #5620.

## Checklist

- [X] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test (especially base/) or added coverage to integration test
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: Robert Müller <robytemueller@gmail.com>

src/game/editor/editor.cpp

@@ -4499,6 +4499,7 @@ void CEditor::RenderFileDialog()
 	{
 		if(IsDir) // folder
 		{
+			m_aFileDialogFilterString[0] = '\0';
 			if(str_comp(m_vpFilteredFileList[m_FilesSelectedIndex]->m_aFilename, "..") == 0) // parent folder
 			{
 				if(fs_parent_dir(m_pFileDialogPath))