Don't dereference invalid iterator in wxDateTime::ParseDate().

If the string passed to this method contained only spaces (possibly 0 of them,
i.e. was empty) we would dereference the end string iterator. Fix this by
adding an explicit test for "p != pEnd".

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63060 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datetimefmt.cpp

@@ -1559,7 +1559,7 @@ wxDateTime::ParseDate(const wxString& date, wxString::const_iterator *end)
     const wxString::const_iterator pEnd = date.end();
 
     wxString::const_iterator p = pBegin;
-    while ( wxIsspace(*p) )
+    while ( p != pEnd && wxIsspace(*p) )
         p++;
 
     // some special cases