added wxVaCopy() and use it to fix wxVsnprintf() crash (see bug 1017651)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@29604 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/string.cpp

@@ -1727,7 +1727,12 @@ int wxString::PrintfV(const wxChar* pszFormat, va_list argptr)
                 return -1;
             }
 
-            len = wxVsnprintf(buf, size, pszFormat, argptr);
+            // wxVsnprintf() may modify the original arg pointer, so pass it
+            // only a copy
+            va_list argptrcopy;
+            wxVaCopy(argptrcopy, argptr);
+            len = wxVsnprintf(buf, size, pszFormat, argptrcopy);
+            va_end(argptrcopy);
 
             // some implementations of vsnprintf() don't NUL terminate
             // the string if there is not enough space for it so