terra::merge & NA handling

[jmmonnet]

Hello,
I noticed that in the latest versions of the terra package (1.7.3 and 1.7.6) the NA values are not handled by terra::merge. A reproducible example can be found from a previous issue on the same topic. #160.
Thank you for this great package !

[rhijmans]

Thanks very much for reporting. I believe it is fixed again. I think I tried to speed up the algorithm and re-introduced this bug. Very annoying; I have now added a test that should detect this.