On cpp files with no headers hte check was stuck in the loop

[Iximiel]

Description

@GiovanniBussi pointed me where to search:

there was this
while((getline < cppfile)>=0) that was stuck (getline returns 0 when the file ends).

In #1183 I created the perfected condition to make this an infinite loop: a .cpp with no includes

And here I added that check.

Target release

I would like my code to appear in release v2.9

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.