Dynmap does not render bottom of edge-chunks in Surface-perspective

[ireun]

Issue Description: Dynmap sample issue description. This description would include as much and as little detail necessary for us to understand the issue in its entirety.

• Dynmap Version: Dynmap-3.7-beta-10-spigot
• Server Version: paper-1.21.4-232.jar
• Pastebin of Configuration.txt: https://gist.github.com/ireun/14d00c5595c9a948f653fe2a0f845f90
• Server Host (if applicable): nope
• Pastebin of crashlogs or other relevant logs: nope
• Other Relevant Data/Screenshots: I'm using this texture pack and these plugins and my map is from alpha .8
• Steps to Replicate: A player moves somewhere where chunks are not yet generated, dynmap generates the map, but does not generate bottom of the chunks in Surface (angle) map view, fullrender resolves this issue

[x] I have looked at all other issues and this is not a duplicate
[x] I have been able to replicate this

[ireun]

I wish there was a 'fix-edge' command, that would re-render just the edge-chunks..