[SHELL32] Fix "Open With..." spamming registry MRU keys. (#2685)

CORE-16981

The problem:
============

- When opening "Open With..." dialog for a given file format, multiple MRU items are appended to registry : 2 items written, even if dialog is closed "cancel".
- Expected behavior : 1 MRU item if execute is selected and 0 MRU if cancel is selected.

Fix:
====

- MRU item to be added when "Execute" is selected only.
- Once added, set the presence flag to avoid multiple MRU items being added later.

dll/win32/shell32/COpenWithMenu.cpp

@@ -534,8 +534,6 @@ VOID COpenWithList::LoadFromProgIdKey(HKEY hKey, LPCWSTR pwszExt)
         {
             StringCbCopyW(pApp->wszCmd, sizeof(pApp->wszCmd), wszCmd);
             SetRecommended(pApp);
-            if (!pApp->bMRUList)
-                AddAppToMRUList(pApp, pwszExt);
         }
     }
 }
@@ -653,6 +651,9 @@ BOOL COpenWithList::AddAppToMRUList(SApp *pApp, LPCWSTR pwszFilename)
         /* Insert the entry */
         AddMRUStringW(hList, pApp->wszFilename);
 
+        /* Set MRU presence */
+        pApp->bMRUList = TRUE;
+
         /* Close MRU list */
         FreeMRUList(hList);
     }