Fix typo

Change-Id: Ib1b8341776ed79c85cd1f8287c06a9fe8ed8ca3d
Reviewed-on: https://gerrit.libreoffice.org/71389
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

sc/source/core/data/postit.cxx

@@ -1017,7 +1017,7 @@ void ScPostIt::CreateCaptionFromInitData( const ScAddress& rPos ) const
     /*  This function is called from ScPostIt::Clone() when copying cells
         to the clipboard/undo document, and when copying cells from the
         clipboard/undo document. The former should always be called first,
-        so if called in an clipboard/undo document, the caption should have
+        so if called in a clipboard/undo document, the caption should have
         been created already. However, for clipboard in case the
         originating document was destructed a new caption has to be
         created. */