take legend font attributes from existing font

src/args.jl

@@ -1968,6 +1968,8 @@ function _update_subplot_legend(sp::Subplot, plotattributes_in)
                 haskey(_match_map, lk) ? sp[lk] :
                 haskey(plotattributes_in, :legend_font) ?
                 getproperty(plotattributes_in[:legend_font], k) :
+                haskey(sp.attr, :legend_font) ?
+                getproperty(sp.attr[:legend_font], k) :
                 default(plotattributes_in, lk)
         ) for k in (:family, :pointsize, :valign, :halign, :rotation, :color)
     )

test/test_defaults.jl

@@ -76,6 +76,11 @@ end # testset
     @test p[1][:legend_background_color] == RGBA{Float64}(0.0, 1.0, 1.0, 1.0)
     @test p[1][:legend_foreground_color] == RGBA{Float64}(0.0, 0.5019607843137255, 0.0, 1.0)
 
+    #remember settings
+    plot(legend_font_pointsize = 20)
+    sp = plot!(label = "R")[1]
+    @test Plots.legendfont(sp).pointsize == 20
+
     #setting whole font
     sp = plot(
         1:5,