Only set undefined axes when drawn

[maxrjones]

Description of proposed changes

Fixes these two examples:

gmt basemap -R0/1/0/1 -JX5c -B+t"ABC" -png map

gmt begin colorbar png
gmt makecpt -Cbatlow -T0/10/1
gmt basemap -R20/30/-10/10 -B
gmt colorbar
gmt end show

Fixes #4955 (partly)

Reminders

• Make sure that your code follows our style. Use the other functions/files as a basis.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Describe changes to function behavior and arguments in a comment below the function declaration.
• If adding new functionality, add a detailed description to the documentation and/or an example.

[maxrjones]

A few tests fail. ex16.sh, ex39.sh, and ex43.sh seem to relate to changes in the map frame pen. categoricalcpt.sh now has labels on the colorbar; the reference file for this was not updated by the themes merge.

[PaulWessel]

Let me know what issues you may want me to look at, i.e., the problems reported by Dongdong.

[maxrjones]

Let me know what issues you may want me to look at, i.e., the problems reported by Dongdong.

I haven't started looking at any of the other issues yet. Would you want to look into the automatic frame intervals changes?

We can update any PostScript files after all the various issues get resolved, since the plots may change each time.

[PaulWessel]

OK, just started trying to deal with

coast -Rd -JKf12c -Bafg -Ggreen -png map

first.