cid 703925 : strncpy can lead to non-null terminated string

Change-Id: Idfe2278d0008715a2e0f06d60df9af430e4df25c
Reviewed-on: https://gerrit.libreoffice.org/874Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>

vcl/source/fontsubset/cff.cxx

@@ -2051,7 +2051,8 @@ bool CffSubsetterContext::emitAsType1( Type1Emitter& rEmitter,
     if( !*pFontName ) {
         if( mnFontNameSID) {
             // get the fontname directly if available
-            strncpy( pFontName, getString( mnFontNameSID), sizeof(rEmitter.maSubsetName));
+            strncpy( pFontName, getString( mnFontNameSID), sizeof(rEmitter.maSubsetName) - 1);
+            pFontName[sizeof(rEmitter.maSubsetName) - 1] = 0;
         } else if( mnFullNameSID) {
             // approximate fontname as fullname-whitespace
             const char* pI = getString( mnFullNameSID);