When trying to set a custom project profile image while the PHP GD extension is not installed, use the same logic which already exists in PhabricatorFilesComposeAvatarBuiltinFile.php to set the default project image. This stills display an unhelpful error message This server only supports these image formats: . but avoids an exception trying to call GD's imagecreatefromstring().
EXCEPTION: (Error) Call to undefined function imagecreatefromstring() at [<phorge>/src/applications/files/builtin/PhabricatorFilesComposeIconBuiltinFile.php:131]
Closes T15326