This fixes a bug that appears if you use HISTOGRAM with READ

[gtribello]

Description

This PR fixes a small bug in the master version of PLUMED that I found when I was reviewing masterclass 21.2.

If you are using driver to analyze the data in colvar file only using the --noatoms option then the pbc information is not transferred to PLUMED and you get a segmentation fault. As you can see I have resolved this problem in KDE.h by checking if the PbcAction is a null pointer and not calling any function from it if it is.

Target release

I would like my code to appear in release 2.11

Type of contribution

• changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• changes to a module not authored by you
• new module contribution or edit of a module authored by you

Copyright

• I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

• the module I added or modified contains a COPYRIGHT file with the correct license information. Code should be released under an open source license. I also used the command cd src && ./header.sh mymodulename in order to make sure the headers of the module are correct.

Tests

• I added a new regtest or modified an existing regtest to validate my changes.
• I verified that all regtests are passed successfully on GitHub Actions.

[carlocamilloni]

@gtribello This looks fine but we need a regtest that fails before and pass after the change to be sure that the bug is not inadvertently reintroduced in the future

[gtribello]

HI @carlocamilloni

I have added the retest. Here is what happens if you try the test with the master version of PLUMED that doesn't have this fix