#2521 "surface explicit" does not work with "hidden3d"

[Eric Price]

set surface implicit
set nohidden3d
splot '<echo -e "#\\n1\\n2\\n3\\n\\n1\\n2\\n3\\n"' using 0:1:0 with linespoints title "this draws as a surface"
pause -1

set surface explicit
set nohidden3d
splot '<echo -e "#\\n1\\n2\\n3\\n\\n1\\n2\\n3\\n"' using 0:1:0 with linespoints title "this draws as two lines"
pause -1

set surface explicit
set hidden3d
splot '<echo -e "#\\n1\\n2\\n3\\n\\n1\\n2\\n3\\n"' using 0:1:0 with linespoints title "this should draw as two lines BUG"
pause -1

tested and reproduced with
gnuplot 5.2 patchlevel 2
gnuplot 5.4 patchlevel 4alpha
any terminal

[Eric Price]

issue also happens "with lines"