fix: keep the --from search on one drive

The walk no longer enters another drive mounted below the folder (it is
named instead), /proc, /sys, /dev or a Windows junction, and the root of
the system is refused. from_folder_problem() checks a folder without
reading it. A scanned event reports each folder read, cut short or not.

install.ps1

@@ -11,7 +11,7 @@
 
     $ErrorActionPreference = "Stop"
     $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-    $defaultInstallSha256 = "4b658dc29528e94460995eaf844b1fc1cca9040ffa10cd71ac6656b4db5f1b34"
+    $defaultInstallSha256 = "06fde26aa660b6e28c05010dd4a1de8f1ff1ab891d6ebbe460b670b30b71befd"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }