Use symbolic WAIT_FAILED constant instead of raw -1.

No real changes, just make the code slightly more readable by using a symbolic
constant instead of a magic value.

This also avoids g++ warnings about implicit conversion of a signed value (-1)
to unsigned type (DWORD).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67962 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/utilsexc.cpp

@@ -1010,7 +1010,7 @@ long wxExecute(const wxString& cmd, int flags, wxProcess *handler,
                 wxFAIL_MSG( wxT("unexpected WaitForInputIdle() return code") );
                 // fall through
 
-            case -1:
+            case WAIT_FAILED:
                 wxLogLastError(wxT("WaitForInputIdle() in wxExecute"));
 
             case WAIT_TIMEOUT: