fs: check if ntfsresize actually succeded to shrink filesystem

According to ntfsresize.c, this retuns 0 in case nothing needs to be done.
It should be safe to check for non-zero error and bail out in that case.

src/utils/fs.py

@@ -260,7 +260,10 @@ def _reduce_ntfsresize(partdev):
     if new_size < size:
         cmd_resize = shlex.split(f'ntfsresize -fs {new_size:.0f} {partdev}')
         with open('/tmp/command.log', 'ab', 0) as logfile:
-            subprocess.run(cmd_resize, input='y', stderr=STDOUT, encoding='utf-8')
+            proc_resize = subprocess.run(cmd_resize, input='y', stderr=STDOUT, encoding='utf-8')
+            if proc_resize.returncode != 0:
+                logging.error(f'ntfsresize on {partdev} with {new_size:.0f} failed with {proc_resize.returncode}')
+                return -1
 
     return 0