Fixed programming error (and BCC warning).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15426 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/hashmap.h

@@ -365,7 +365,7 @@ CLASSEXP CLASSNAME \
 { \
 public: \
     CLASSNAME() { } \
-    KEY_T operator()( PAIR_T pair ) const { return pair.first; } \
+    const KEY_T& operator()( const PAIR_T& pair ) const { return pair.first; }\
     \
     /* the dummy assignment operator is needed to suppress compiler */ \
     /* warnings from hash table class' operator=(): gcc complains about */ \