Fixed missing marker in legend when plotting a series whose first ent…

…ry is NaN (#4328)

* Changed function `gr_add_legend` to call `gr_draw_marker` instead of `gr_draw_markers`, since a legend entry only has one marker (if any).

* Resolved conflict in  (kept new method of calculating s, sw)

* Ran JuliaFormatter, reformatted long function call of  to span multiple lines

src/backends/gr.jl

@@ -1139,6 +1139,7 @@ function gr_add_legend(sp, leg, viewport_plotarea)
                 if series[:markershape] !== :none
                     ms = first(series[:markersize])
                     msw = first(series[:markerstrokewidth])
+                    shape = Plots._cycle(series[:markershape], 1)
                     s, sw =
                         min.(
                             maxmarkersize,
@@ -1149,7 +1150,16 @@ function gr_add_legend(sp, leg, viewport_plotarea)
                                 0, 0.8 * sp[:legend_font_pointsize] * msw / 8
                             end,
                         )
-                    gr_draw_markers(series, xpos - leg.width_factor * 2, ypos, clims, s, sw)
+                    gr_draw_marker(
+                        series,
+                        xpos - leg.width_factor * 2,
+                        ypos,
+                        clims,
+                        1,
+                        s,
+                        sw,
+                        shape,
+                    )
                 end
 
                 lab = series[:label]