Loading SLSTR composite doesn't respect the view

[simonrp84]

Describe the bug
SLSTR data is in two views, oblique and nadir. By default, Satpy loads nadir data.
If the user requires oblique view data they can request this, which works well when a single channel is requested. However, if the user requests and oblique view composite then instead satpy returns the nadir view.

To Reproduce

scn = Scene(files, reader='slstr_l1b')
scn.load([DataQuery(name='natural_color', view='oblique')])
scn.save_datasets(filename='oblique.tif')

scn2 = Scene(files, reader='slstr_l1b')
scn2.load([DataQuery(name='natural_color', view='nadir')])
scn2.save_datasets(filename='nadir.tif')

Expected behavior
The above code should create two tif files, one with nadir view data and one with the oblique view.

Actual results
Both of the tif files contain the nadir view data.

[simonrp84]

This is fixed in #1533, will close the issue once it's merged.