common: Fix return value and typos in flatpak_switch_symlink_and_remove

One error path returned -1 instead of FALSE. Since gboolean is gint,
-1 is truthy and the caller would skip error handling.

Assisted-by: Claude:opus-4.6
Helps: https://github.com/flatpak/flatpak/security/advisories/GHSA-99wv-m8rp-g58x

common/flatpak-utils.c

@@ -983,10 +983,10 @@ flatpak_str_is_alphanumeric (const char *arg)
 }
 
 /* This atomically replaces a symlink with a new value, removing the
- * existing symlink target, if it exstis and is different from
+ * existing symlink target, if it exists and is different from
  * @target. This is atomic in the sense that we're guaranteed to
  * remove any existing symlink target (once), independent of how many
- * processes do the same operation in parallele. However, it is still
+ * processes do the same operation in parallel. However, it is still
  * possible that we remove the old and then fail to create the new
  * symlink for some reason, ending up with neither the old or the new
  * target. That is fine if the reason for the symlink is keeping a
@@ -1038,7 +1038,7 @@ flatpak_switch_symlink_and_remove (const char *symlink_path,
           if (old_target == NULL)
             return FALSE;
 
-          /* Don't remove old file if its the same as the new one */
+          /* Don't remove old file if it's the same as the new one */
           if (strcmp (old_target, target) != 0)
             {
               if (flatpak_str_is_alphanumeric (old_target))
@@ -1058,7 +1058,7 @@ flatpak_switch_symlink_and_remove (const char *symlink_path,
         {
           glnx_set_error_from_errno (error);
           unlink (tmp_path);
-          return -1;
+          return FALSE;
         }
       unlink (tmp_path);