graph_draw(): fix issue with property maps being changed

This fixes issue #658
8 jobs for master in 587 minutes and 38 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Test
passed job_clang_amd64 #4640
amd64

09:47:38

passed job_gcc_amd64 #4641
amd64

04:22:37

failed job_clang_amd64 #4635
amd64

failed job_clang_amd64 #4632
amd64

failed job_clang_amd64 #4613
amd64

02:20:25

failed job_gcc_amd64 #4636
amd64

failed job_gcc_amd64 #4631
amd64

failed job_gcc_amd64 #4612
amd64

02:20:23