Show httpbin output if the test failed, not if it succeeded

This output is mostly useful for diagnosing errors, so it's not very
useful to show it only after successful test completion in after_test
command.

appveyor.yml

@@ -84,6 +84,3 @@ test_script: c:\projects\wxwidgets\build\tools\appveyor-test.bat
 after_test:
 - ps: |
     Stop-Job -Name wx_httpbin
-    Write-Output "--- httpbin output ---"
-    Get-Content c:\projects\wxwidgets\httpbin.log
-    Write-Output "--- httpbin output end ---"

build/tools/appveyor-test.bat

@@ -59,4 +59,7 @@ goto :eof
 echo.
 echo !!! Non-GUI test failed.
 echo.
+echo --- httpbin output ---
+type c:\projects\wxwidgets\httpbin.log
+echo --- httpbin output end ---
 goto :eof