Compile even less code when wxUSE_WEBREQUEST==0 in the test

Move the check slightly higher, there is no need to include the headers
if we're not going to compile any tests anyhow.

tests/net/webrequest.cpp

@@ -21,6 +21,8 @@
     #include "wx/wx.h"
 #endif // WX_PRECOMP
 
+#if wxUSE_WEBREQUEST
+
 #include "wx/webrequest.h"
 #include "wx/filename.h"
 #include "wx/wfstream.h"
@@ -34,8 +36,6 @@
 // an environment variable, e.g.:
 //   WX_TEST_WEBREQUEST_URL=https://httpbin.org
 
-#if wxUSE_WEBREQUEST
-
 class RequestFixture
 {
 public: