coverity#1441442 Unintended sign extension

Change-Id: Id0286f34ccc387dd148e42b83e8f62aacfb54219
Reviewed-on: https://gerrit.libreoffice.org/63535
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sc/source/filter/inc/ftools.hxx

@@ -99,7 +99,7 @@ inline void set_flag( Type& rnBitField, Type nMask, bool bSet = true )
 template< typename Type, typename InsertType >
 void insert_value( Type& rnBitField, InsertType nValue, sal_uInt8 nStartBit, sal_uInt8 nBitCount )
 {
-    unsigned long nMask = ((1UL << nBitCount) - 1);
+    unsigned int nMask = ((1U << nBitCount) - 1);
     Type nNewValue = static_cast< Type >( nValue & nMask );
     rnBitField = (rnBitField & ~(nMask << nStartBit)) | (nNewValue << nStartBit);
 }