Fall back to using LIST if NAMESPACE answer is malformed or otherwise problematic...

Fall back to using LIST if NAMESPACE answer is malformed or otherwise problematic.  This still doesn't account for situations where the NAMESPACE or LIST answer can't be parsed correctly.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@14302 7612ce4b-ef26-0410-bec9-ea0150e637f0