regression (crash) in showing empty method list

[vtjnash]

julia> struct NOP{P} end

julia> methods(NOP)
# 0 methods for type constructorError showing value of type Base.MethodList:
ERROR: BoundsError: attempt to access 0-element Vector{Method} at index [1]
Stacktrace:
  [1] getindex
    @ ./essentials.jl:13 [inlined]
  [2] show_method_table(io::IOContext{Base.TTY}, ms::Base.MethodList, max::Int64, header::Bool)
    @ Base ./methodshow.jl:296
  [3] show_method_table
    @ ./methodshow.jl:282 [inlined]
  [4] show(io::IOContext{Base.TTY}, #unused#::MIME{Symbol("text/plain")}, ms::Base.MethodList)
    @ Base ./methodshow.jl:342

julia> @test sprint(show, Base.MethodList(Method[], typeof(NOP).name.mt)) isa String

[ianatol]

Bisected to b2b8ce8 (#45069)

Specifically this line assumes a non-empty MethodList

CC @Seelengrab