View Results Tree:When reloading results from XML, content type is not filled in SampleResult

**UbikLoadPack support** ([Bug 56983](https://bz.apache.org/bugzilla//show_bug.cgi?id=56983&redirect=false)):
Hello,
We noticed the following bug when using this scenario:
- Make a load test that generates an XML (View Results Tree with filename + All fields for XML checked)
- Once test is finished load XML generated file
- As you will see Content-Type is not initialized

Created attachment [Reloaded.png](https://apache.github.io/jmeter-bugzilla-attachments/83/56983/32022/Reloaded.png): Reloaded

Severity: normal
OS: All