When disabling all protocols without enabling any, the resulting
set of allowed protocols remained the default set. Clearing the
allowed set before inspecting the passed value from --proto make
the set empty even in the errorpath of no protocols enabled.
Co-authored-by: Dan Fandrich <dan@telarity.com>
Reported-by: Dan Fandrich <dan@telarity.com>
Reviewed-by: Daniel Stenberg <daniel@haxx.se>
Closes: #13004
