fix bug in DocumentSettings::LoadList when testing result of lastIndexOf

managed to trigger it in a flat ODF test document of mine.

I suspect that this might have something to do with one of the various
conversions to OUString, the old String APIs might have returned -LARGE_INTEGER
instead of -1.

code was introduced in commit
    cbcfda9b
    Author: Michael Meeks <michael.meeks@novell.com>
    Date:   Mon Sep 5 17:22:24 2011 +0100
    add XPropertyList enum, factory, and associated cleanup

Change-Id: I39b4715cc12ef6366fe0466786589ef198602a98
Reviewed-on: https://gerrit.libreoffice.org/29473Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>

sd/source/ui/unoidl/UnoDocumentSettings.cxx

@@ -233,7 +233,7 @@ bool DocumentSettings::LoadList( XPropertyListType t, const OUString &rInPath,
 
     sal_Int32 nSlash = rInPath.lastIndexOf('/');
     OUString aPath, aName;
-    if (nSlash < -1)
+    if (nSlash < 0)
         aName = rInPath;
     else {
         aName = rInPath.copy( nSlash + 1 );