`opnorm(::SymTridiagonal,1 or Inf)` fails for 2x2 argument

[RalphAS]

This bug was introduced after v1.11.

Example:

julia-1.12> opnorm(SymTridiagonal([1.0,1.0],[0.0]),1)
ERROR: ArgumentError: reducing over an empty collection is not allowed; consider supplying `init` to the reducer
Stacktrace:
  [1] _empty_reduce_error()
    @ Base ./reduce.jl:311
  [2] mapreduce_empty(f::Function, op::Base.BottomRF{typeof(max)}, T::Type)
    @ Base ./reduce.jl:313
  [3] reduce_empty(op::Base.MappingRF{LinearAlgebra.var"#_opnorm1Inf##2#_opnorm1Inf##3", Base.BottomRF{…}}, ::Type{Tuple{…}})
    @ Base ./reduce.jl:350
  [4] reduce_empty_iter
    @ ./reduce.jl:373 [inlined]
  [5] reduce_empty_iter
    @ ./reduce.jl:372 [inlined]
  [6] foldl_impl
    @ ./reduce.jl:41 [inlined]
  [7] mapfoldl_impl
    @ ./reduce.jl:36 [inlined]
  [8] mapfoldl
    @ ./reduce.jl:167 [inlined]
  [9] mapreduce
    @ ./reduce.jl:299 [inlined]
 [10] _opnorm1Inf
    @ /scratch/build/julia-1.12.0-rc1/share/julia/stdlib/v1.12/LinearAlgebra/src/tridiag.jl:1128 [inlined]
 [11] opnorm(A::SymTridiagonal{Float64, Vector{Float64}}, p::Int64)
    @ LinearAlgebra /scratch/build/julia-1.12.0-rc1/share/julia/stdlib/v1.12/LinearAlgebra/src/special.jl:626
 [12] top-level scope
    @ REPL[10]:1
Some type information was truncated. Use `show(err)` to see complete types.