tdf#72205 when saving changes, mark we did a prepareClose

Change-Id: I8a86447bdd227621ff7b0b3551798ee343379c74
Reviewed-on: https://gerrit.libreoffice.org/19437Reviewed-by: Eike Rathke <erack@redhat.com>
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>
(cherry picked from commit b392270d)

svx/source/form/fmshell.cxx

@@ -276,6 +276,8 @@ bool FmFormShell::PrepareClose(bool bUI)
                         {
                             case RET_NO:
                                 bModified = false;
+                                // fallthrough to next case
+                            case RET_YES:
                                 GetImpl()->didPrepareClose( true );
                                 break;