daemon: fix low severity bugs in debug, file, and blkid (#315)

- debug.c: fix memory leak of out buffer on opendir failure in
  debug_fds. After fclose on open_memstream, the out buffer is
  allocated and must be freed.

- file.c: add missing reply_with_perror on strdup failure in
  do_zfile, so callers get a proper error message instead of
  silent NULL return.

- blkid.c: fix wrong error variable used at command_failed label
  in test_blkid_p_i_opt. The second commandr stores its error in
  err2, but goto command_failed would report err from the first
  command. Inline the error reporting with the correct variable.

Co-authored-by: Claude <noreply@anthropic.com>

daemon/blkid.c

@@ -112,8 +112,10 @@ test_blkid_p_i_opt (void)
   }
 
   r = commandr (NULL, &err2, "blkid", "-i", NULL);
-  if (r == -1)
-    goto command_failed;
+  if (r == -1) {
+    reply_with_error ("could not run 'blkid' command: %s", err2);
+    return -1;
+  }
 
   if (strstr (err2, "invalid option --")) {
     return 0;

daemon/debug.c

@@ -164,6 +164,7 @@ debug_fds (const char *subcmd, size_t argc, char *const *const argv)
   if (!dir) {
     reply_with_perror ("opendir: /proc/self/fd");
     fclose (fp);
+    free (out);
     return NULL;
   }
 

daemon/file.c

@@ -501,7 +501,10 @@ do_zfile (const char *method, const char *path)
   if (len > 0 && line[len-1] == '\n')
     line[len-1] = '\0';
 
-  return strdup (line);
+  char *ret = strdup (line);
+  if (ret == NULL)
+    reply_with_perror ("strdup");
+  return ret;
 }
 
 int64_t