don't always show integer part for fraction formats with hard denom fdo#56205

fixes bug when you have a fraction format with a forced denominator e.g. '?/5'
which showed the integer part of the fraction ( as if the format was '# ?/5' )
but even without the space
e.g. before fix
pi 3.14159265358979 with format '?/8' would be shown as "31/8"

after the fix
   3.14159265358979 with format '?/8' would be shown as "25/8"

Change-Id: I1feb8b78af94b90db1bcc30da248077243dd8dfc
Reviewed-on: https://gerrit.libreoffice.org/1047Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>

svl/source/numbers/zforscan.cxx

@@ -1595,7 +1595,9 @@ xub_StrLen ImpSvNumberformatScan::FinalScan( String& rString )
                                 nCounter = nCntPost;
                             else if (nCntPre)
                                 nCounter = nCntPre;
-                            if (!nCntPre)
+                            // don't artificially increment nCntPre
+                            // for forced denominator
+                            if ( ( eScannedType != NUMBERFORMAT_FRACTION ) && (!nCntPre) )
                                 nCntPre++;
                         }
                     }