ofz#3457 Unknown Read

similar to

commit 35bac83e
Date:   Mon Aug 7 19:24:37 2017 +0100

    ofz#2877: crash in SVTB16Short

Change-Id: Idc2ca89647a5e17484effaca49afce349b98f0a3
Reviewed-on: https://gerrit.libreoffice.org/42622Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/filter/ww8/ww8scan.cxx

@@ -3547,8 +3547,7 @@ SprmResult WW8PLCFx_SEPX::HasSprm( sal_uInt16 nId, sal_uInt8 n2nd ) const
         return SprmResult();
 
     sal_uInt8* pSp = pSprms.get();
-
-    sal_uInt16 i=0;
+    size_t i = 0;
     while (i + maSprmParser.MinSprmLen() <= nSprmSiz)
     {
         // Sprm found?