Load algorithm loading nexus if can't find the specified file extension for a given run

[RichardWaiteSTFC]

Describe the bug
Load algorithm loading nexus if can't find the specified file extension (e.g. .s02)

To Reproduce
(1) Make sure archive search is enabled in Manage user directories
(2) Run this script

ws = Load(Filename='PEARL00116374.s09')
algs = ws.getHistory()
print('Filename = ', algs[0].getProperty("Filename").value)

it will print out
['\\\\isis.cclrc.ac.uk\\inst$\\ndxpearl\\instrument\\data\\cycle_21_1\\PEARL00116374.nxs']
i.e. it loads the nexus

Expected behavior
Throw an error for file not found

[RichardWaiteSTFC]

Having considered this again I think throwing an error, though intuitive, would be quite a radical change in behaviour of the Load algorithm which is quite important! Perhaps a warning instead?