tdf#102370 Correctly export to Excel exponent without sign

Exponent without sign in scientific notation is coded in Excel with a minus
sign replacing plus sign: 0.00E-00 for instance
This format is already correctly treated in Calc but was not correctly
exported to Excel or ODF

Change-Id: Ide117b04e0eb887c6cdd6699ae8ec723d1d29d50
Reviewed-on: https://gerrit.libreoffice.org/29198Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>

svl/source/numbers/zformat.cxx

@@ -4806,9 +4806,12 @@ OUString SvNumberformat::GetMappedFormatstring( const NfKeywordTable& rKeywords,
                         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( "+" );
+                        if ( pStr[j].getLength() > 1 && pStr[j][1] == '+' )
+                            aStr.append( "+" );
+                        else
+                        // tdf#102370: Excel code for exponent without sign
+                            aStr.append( "-" );
                         break;
                     case NF_SYMBOLTYPE_DATESEP :
                         aStr.append( rLocWrp.getDateSep() );

xmloff/source/style/xmlnumfe.cxx

@@ -1321,8 +1321,9 @@ void SvXMLNumFmtExport::ExportPart_Impl( const SvNumberformat& rFormat, sal_uInt
                 case NF_SYMBOLTYPE_EXP:
                     bExpFound = true;           // following digits are exponent digits
                     bInInteger = false;
-                    if ( pElemStr && pElemStr->getLength() == 1 )
-                        bExpSign = false;       // for 0.00E0
+                    if ( pElemStr && ( pElemStr->getLength() == 1
+                                  || ( pElemStr->getLength() == 2 && (*pElemStr)[1] == '-' ) ) )
+                        bExpSign = false;       // for 0.00E0 or 0.00E-00
                     break;
                 case NF_SYMBOLTYPE_CURRENCY:
                     bCurrFound = true;