prevent spurious PHP notice on settings wipe

git-svn-id: https://plugins.svn.wordpress.org/updraftplus/trunk@821877 b8457f37-d9ea-0310-8a92-e5e31aec5664
prevent over-long pathname being used on unzip

git-svn-id: https://plugins.svn.wordpress.org/updraftplus/trunk@821988 b8457f37-d9ea-0310-8a92-e5e31aec5664