[common] fix: some backend commands could hang when require user interaction

CHANGELOG.md

@@ -13,6 +13,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - always displaying the "any file filter" (*) as the last option for file chooser components [#193](https://github.com/vinifmor/bauh/issues/193)
 
 ### Fixes
+- Arch
+  - not able to install packages when launched by the root user
 - AppImage
     - not displaying the filter for any kind of file (*) when updating imported AppImages [#193](https://github.com/vinifmor/bauh/issues/193)
 - Flatpak

bauh/commons/system.py

@@ -89,15 +89,13 @@ class SimpleProcess:
         args = {
             "stdout": subprocess.PIPE,
             "stderr": subprocess.STDOUT,
+            "stdin": stdin if stdin else subprocess.DEVNULL,
             "bufsize": -1,
             "cwd": cwd,
             "env": gen_env(global_interpreter, lang, extra_paths=extra_paths),
             "shell": self.shell
         }
 
-        if stdin:
-            args['stdin'] = stdin
-
         return subprocess.Popen(args=[' '.join(cmd)] if self.shell else cmd, **args)