Fix standard nullhypo case adaptive scale (spreadNH)

[dehann]

see lines (introduced by #791 ) :

IncrementalInference.jl/src/ApproxConv.jl

Lines 139 to 140 in 417e503

	# FIXME use adaptive scale, see #802
	msst_ = 0 < sum(1e-10 .< msst) ? maximum(msst) : 1.0

note this is an expansion beyond initial work for consolidating #237