Add distance validation in merge function and clamp grid coords

[Freeslugga]

Closes #3155 - Crash when merging brush layer into boolean layer in debug

both changes to rs files in node-graph, merge handling was improper, causing a panic with certain data types. Also clamped the grid points to avoid invalid data being passed.

[Freeslugga]

Currently the crash is fixed, but when you add a brush layer to the boolean group it rescales and moves the brush layer to the point where it is invisible. You are able to reset the scale and location via the properties menu and the brush re-appears.

[Freeslugga]

Not sure where the transforms are taking place, I can open as a separate issue if this is merged.

[Freeslugga]

@Keavon This is my first contribution to an open-source project, please let me know if you have any direct feedback to better assist my journey with contributing!

[Keavon]

Thanks, I will be busy for the next day or two as I get the next release out, then I'll try to take a look. Feel free to take on more issues in the meantime.