MM UNO always print single files to printer

Fix a missing hunk from e0ad036e,
which causes assertion, if MM is used via UNO.

Thanks to Alex Kempshall, finding the assertion when testing MM.

Change-Id: Ia0cd6053838adc6f0a4ce93902f06423849bf851

sw/source/uibase/uno/unomailmerge.cxx

@@ -693,7 +693,7 @@ uno::Any SAL_CALL SwXMailMerge::execute(
             // #i25686# printing should not be done asynchronously to prevent dangling offices
             // when mail merge is called as command line macro
             aMergeDesc.aPrintOptions = m_aPrintSettings;
-            aMergeDesc.bCreateSingleFile = false;
+            aMergeDesc.bCreateSingleFile = true;
         }
         break;
     case MailMergeType::SHELL: