issparse is not defined but is requested for a view's parent #486

Describe the bug 🐞

On certain operations, issparse(::SubArray) is called, and it calls issparse on the parent, but it's not defined in the case of AbstractVectorOfArray.

Expected behavior

issparse(::SubArray) is defined, to false.

Error & Stacktrace ⚠️

> U = mapreduce(u -> view(u, :, :), hcat, us)
MethodError: no method matching issparse(::ODESolution{...})

Additional context

Solution:

import SparseArrays: issparse
issparse(::AbstractVectorOfArray) = false