Fix wrong indentation in wxDDE code

No real changes, but this avoids warnings about possibly wrong code from the
latest g++ versions.

Also add braces around a multiline "if" statement body.

src/msw/dde.cpp

@@ -885,6 +885,7 @@ _DDECallback(WORD wType,
                     if (data)
                     {
                         if (user_size == wxNO_LEN)
+                        {
                             switch (wFmt)
                             {
                                 case wxIPC_TEXT:
@@ -897,6 +898,7 @@ _DDECallback(WORD wType,
                                 default:
                                     user_size = 0;
                             }
+                        }
 
                         HDDEDATA handle = DdeCreateDataHandle(DDEIdInst,
                                                               (LPBYTE)data,