Add wxAutomationInstance_SilentIfNone flag for wxMSW OLE code.

This flag allows to suppress the error message in case there are no currently
running instances of this object and can be useful if the caller doesn't know
in advance whether it's available or not.

Closes #12734.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66967 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/msw/ole/automtn.h

@@ -31,7 +31,15 @@ enum wxAutomationInstanceFlags
         instance failed, we should call wxAutomationObject::CreateInstance() to
         create a new one.
      */
-    wxAutomationInstance_CreateIfNeeded = 1
+    wxAutomationInstance_CreateIfNeeded = 1,
+
+    /**
+        Do not show an error message if no existing instance is currently
+        running.
+
+        All other errors will still be reported as usual.
+     */
+    wxAutomationInstance_SilentIfNone = 2
 };
 
 
@@ -134,6 +142,10 @@ public:
 
         If attaching to an existing object failed and @a flags includes
         wxAutomationInstance_CreateIfNeeded flag, a new object will be created.
+        Otherwise this function will normally log an error message which may be
+        undesirable if the object may or may not exist. The
+        wxAutomationInstance_SilentIfNone flag can be used to prevent the error
+        from being logged in this case.
 
         Returns @true if a pointer was successfully retrieved, @false
         otherwise.