implemented wxMemoryInputStream::CanRead() and added tests for CanRead() to all stream tests

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44872 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

tests/streams/ffilestream.cpp

@@ -47,6 +47,7 @@ public:
         CPPUNIT_TEST(Input_Read);
         CPPUNIT_TEST(Input_Eof);
         CPPUNIT_TEST(Input_LastRead);
+        CPPUNIT_TEST(Input_CanRead);
         CPPUNIT_TEST(Input_SeekI);
         CPPUNIT_TEST(Input_TellI);
         CPPUNIT_TEST(Input_Peek);