tdf#92037 fix dragging DataSources field into document

Bug introduced by my commit fb14be5f
"create new 'enum class' SotClipboardFormatId to unify types"

Change-Id: I7347fb9e653077205476e2b0c2b8107dc9caae0e
Reviewed-on: https://gerrit.libreoffice.org/16396Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>

sot/source/base/exchange.cxx

@@ -343,7 +343,7 @@ bool SotExchange::GetFormatDataFlavor( SotClipboardFormatId nFormat, DataFlavor&
     {
         tDataFlavorList& rL = InitFormats_Impl();
 
-        unsigned i = static_cast<int>(nFormat) - static_cast<int>(SotClipboardFormatId::USER_END) + 1;
+        unsigned i = static_cast<int>(nFormat) - static_cast<int>(SotClipboardFormatId::USER_END) - 1;
 
         if( rL.size() > i )
         {
@@ -377,7 +377,7 @@ OUString SotExchange::GetFormatMimeType( SotClipboardFormatId nFormat )
     {
         tDataFlavorList& rL = InitFormats_Impl();
 
-        unsigned i = static_cast<int>(nFormat) - static_cast<int>(SotClipboardFormatId::USER_END) + 1;
+        unsigned i = static_cast<int>(nFormat) - static_cast<int>(SotClipboardFormatId::USER_END) - 1;
 
         if( rL.size() > i )
             sMimeType = rL[ i ]->MimeType;