Profiler - Unable to load in captures from 2017.4 or earlier

When loading in old data captures we should show the message 'Profiler data captured in an old version of Unity which is no longer supported. The data will load correctly in Unity 2018.4'. This doesn't look to happen for very old captures and instead shows 'Profiler data stream has invalid signature. Was this Profiler data captured in a newer Unity version?'

When trying to load in data from 5.6
[Internal link]
[Internal link]

Loading data from 2017.4
[Internal link]
[Internal link]

Steps to reproduce:

1.  Load data in from 5.6
2.  Notice error about 'Profiler data stream has invalid signature. Was this Profiler data captured in a newer Unity version?'
3.  Load in data from 2017.4
4. Notice it correctly says 'Profiler data captured in an old version of Unity which is no longer supported. The data will load correctly in Unity 2018.4.'

Actual results: Loading 5.6 seems to not be handled correctly

Expected results: loading 5.6 data should show the same message as loading 2017.4