sfx2: improve reported error message in SfxBaseModel::impl_store()

Old: com.sun.star.io.IOException: SfxBaseModel::impl_store <file:///c:/lo/bugs/saved.xhtml> failed: 0x507

New: com.sun.star.io.IOException: SfxBaseModel::impl_store <file:///c:/lo/bugs/saved.xhtml> failed: 0x507(Error Area:Io Class:Access Code:1287)

It's much easier to find the relevant define in include/vcl/errcode.hxx based
on the new output.

Change-Id: I7d98dcf1ead10264672b45de570e51a153090499
Reviewed-on: https://gerrit.libreoffice.org/47319Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

sfx2/source/doc/sfxbasemodel.cxx

@@ -3013,8 +3013,10 @@ void SfxBaseModel::impl_store(  const   OUString&                   sURL
             SfxGetpApp()->NotifyEvent( SfxEventHint( bSaveTo ? SfxEventHintId::SaveToDocFailed : SfxEventHintId::SaveAsDocFailed, GlobalEventConfig::GetEventName( bSaveTo ? GlobalEventId::SAVETODOCFAILED : GlobalEventId::SAVEASDOCFAILED),
                                                     m_pData->m_pObjectShell.get() ) );
 
+            std::stringstream aErrCode;
+            aErrCode << nErrCode;
             throw task::ErrorCodeIOException(
-                "SfxBaseModel::impl_store <" + sURL + "> failed: " + nErrCode.toHexString(),
+                "SfxBaseModel::impl_store <" + sURL + "> failed: " + OUString::fromUtf8(aErrCode.str().c_str()),
                 Reference< XInterface >(), sal_uInt32(nErrCode));
         }
     }