Tell fasthttp to not set "Content-Length: 0" on non cached content (#107)

fix #97

Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://codeberg.org/Codeberg/pages-server/pulls/107

integration/get_test.go

@@ -59,6 +59,8 @@ func TestGetContent(t *testing.T) {
 	assert.EqualValues(t, "text/html; charset=utf-8", resp.Header.Get("Content-Type"))
 	assert.True(t, getSize(resp.Body) > 100)
 	assert.Len(t, resp.Header.Get("ETag"), 42)
+
+	// TODO: test get of non cachable content (content size > fileCacheSizeLimit)
 }
 
 func TestCustomDomain(t *testing.T) {