Fix/cmake module path

With !1249 (merged) the cmake module path of the source project is temporarily removed. This changes the order of module paths in CMAKE_MODULE_PATH for dependencies that don't have ${proj}_MODULE_PATH, moving them to the front of CMAKE_MODULE_PATH.

This should restore the behaviour to before b1188929 which introduced a change in the order. I think this was just indented to factor out the function and simplify the code but the new code changed the behaviour a bit and introduced many duplicates into the CMAKE_MODULE_PATH which makes it hard to get an overview.