Fix nothing in decrease function (#144)

Author: tmigot

src/utils/increase_decrease.jl

@@ -31,7 +31,7 @@ function decrease(X::PDataKARC, α::T, TR::ARTrustRegion) where {T}
     α2 = max(X.norm_dirs[X.indmin] / X.shifts[X.indmin], eps(T))
   end
 
-  if X.indmin == last & (α2 > targetα)
+  if (isnothing(X.indmin) | isnothing(last) | X.indmin == last) & (α2 > targetα)
     @warn "PreProcessKARC failure: α2=$α2"
   end