tdf#95677 Force sign to exponent for Excel export

Change-Id: I7896d1d064cd92fd45a6b32ac64f534f68213169
Reviewed-on: https://gerrit.libreoffice.org/20064Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>

svl/source/numbers/zformat.cxx

@@ -4861,6 +4861,11 @@ OUString SvNumberformat::GetMappedFormatstring( const NfKeywordTable& rKeywords,
                     case NF_SYMBOLTYPE_THSEP :
                         aStr.append( rLocWrp.getNumThousandSep() );
                         break;
+                    case NF_SYMBOLTYPE_EXP :
+                        // tdf#95677: Excel does not support exponent without sign
+                        aStr.append( rKeywords[NF_KEY_E] );
+                        aStr.append( "+" );
+                        break;
                     case NF_SYMBOLTYPE_DATESEP :
                         aStr.append( rLocWrp.getDateSep() );
                         break;