escape {} into '' for non-standard filenames

archiver/checks/default_preparation_checks.ini

@@ -26,7 +26,7 @@ precondition=find --version | grep 'GNU findutils'
 precondition_failure_msg=Requires GNU find. On mac, you can install it using 'brew install findutils'
 # for every link, resolve path relative to archive dir, if not within archive dir, print absolute
 # note, that the second -exec will only be executed if the previous exec was successful
-check_cmd=find . -type l ! -xtype l -exec sh -c "realpath --relative-base . {} | grep --quiet '^/' " \; -exec echo {} \;
+check_cmd=find . -type l ! -xtype l -exec sh -c "realpath --relative-base . '{}' | grep --quiet '^/' " \; -exec echo {} \;
 success_conditions=EMPTY_OUTPUT
 check_failure_msg=Found symlinks pointing outside the directory tree of {WDIR}. Archives may not be complete.