doc image generator producing errors

[robe]

Note from Greg - ​https://lists.osgeo.org/pipermail/postgis-devel/2018-May/027141.html

  generating ../images/de9im02.png
  convert: non-conforming drawing primitive definition `+' @ error/draw.c/DrawImage/3205.
  convert: non-conforming drawing primitive definition `circle' @ error/draw.c/DrawImage/3605.
  Failure return code (1) from command: convert -size 200x200 xc:none -fill DarkSeaGreen4 -strokewidth 0 -draw "circle 25,51 25, +\260\367^?^?'" -flip tmp1.pngconve\
  rt: non-conforming drawing primitive definition `+' @ error/draw.c/DrawImage/3205.
  convert: non-conforming drawing primitive definition `circle' @ error/draw.c/DrawImage/3605.
  Failure return code (1) from command: convert -size 200x200 xc:none -fill "#00bfff" -strokewidth 0 -draw "circle 75,106 75, +\260\367^?^?'" -flip tmp2.pnggenerati\
  ng ../images/st_azimuth01.png
  convert: non-conforming drawing primitive definition `P\261\260\367^?^?'' @ error/draw.c/DrawImage/3205.

Need to trace when this started happening. I think debbie has similar issue, though may be different. I don't notice a difference in output though.

LAst change to generator.c was at r16296

[komzpa]

Fix: ​https://github.com/postgis/postgis/pull/252

[komzpa]

In 16597:

Fix typo in drawPoint() in doc images generator.

Issue introduced in r16296

Closes #4098
Closes ​https://github.com/postgis/postgis/pull/252