Take raw pointer and not wxSharedPtr<> in SetData()

Using shared pointer seems to be ill-advised here, the stream shouldn't
be shared as it's going to be used by wxWebRequest itself and can't be
used by the application code in parallel, so the ownership transfer
semantics is more appropriate.

We could take a wxScopedPtr<> instead, but wx API takes ownership of raw
pointers everywhere else, so do it here too.

Incidentally fix a bug with calling IsOk() on a possibly null pointer.

tests/net/webrequest.cpp

@@ -178,10 +178,10 @@ TEST_CASE_METHOD(RequestFixture, "WebRequest", "[net][webrequest]")
     SECTION("PUT file data")
     {
         Create("/put");
-        wxSharedPtr<wxInputStream> is(new wxFileInputStream("horse.png"));
+        wxScopedPtr<wxInputStream> is(new wxFileInputStream("horse.png"));
         REQUIRE( is->IsOk() );
 
-        request.SetData(is, "image/png");
+        request.SetData(is.release(), "image/png");
         request.SetMethod("PUT");
         Run();
     }