Related fdo#58774 Alternative dialog Find & Replace for Writer

After having installed the extension from http://extensions.libreoffice.org/extension-center/alternative-dialog-find-replace-for-writer/releases/1.4
I had a crash, extract of bt:
5  0x00002aaad3ee13df in rtl::OUString::copy (this=0x7fffffff2510, beginIndex=147, count=-15) at /home/julien/compile-libreoffice/libreoffice/include/rtl/ustring.hxx:1481
6  0x00002aaad3edc10e in stringresource::StringResourcePersistenceImpl::implScanLocaleNames (this=0x8e2bba0, aContentSeq=uno::Sequence of length 24 = {...})
    at /home/julien/compile-libreoffice/libreoffice/scripting/source/stringresource/stringresource.cxx:1728

So add a quick check to be sure iDot > iSlash

Cherry-picked from d59da701c67074a44abcfebcb7506792d12127ae

Change-Id: I944a852d6cc9a35c451985ac96032f0d848136e8
Reviewed-on: https://gerrit.libreoffice.org/9847
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>