Reminder of issue #9073. "Segmentation fault in coast using -JE and -R+r modifier"

#9104 fixed the crash reported in #9073 with
```
gmt coast -Vd -R6.97229795181/-37.0769712136/278.20744191/7.44518494882r -JE103.989333/1.359211/17.7c -Glightgrey -pdf t
```
But that fix was just a patch that avoids the problem and doesn't solve its root, which is: why `lat1` is NaN.
There is also another malfunctioning with the land shading with disparate reports from different OSs.

Start with the reproduction command in this issue and compare the workaround in #9104 with the original report in #9073. Trace why lat1 becomes NaN and investigate the inconsistent land shading across operating systems; done means the root cause is addressed rather than only avoided, with land shading behaving consistently.

Written by the indexing model from the issue text.