functions with body wipe context.extra

[gdementen]

If there is in the same expression a call to a function with a body and any EvaluableExpression (which gets stored in extra, eg periodic globals, __getitem__ or attribute access), it breaks, because it first evaluates the EvalableExpression, stores it in .extra then calls the function, which wipes .extra and then by the time we try go evaluate the "larger" expression, we can't find the variable storing the EvaluableExpression result.

entities:
    test:
        processes:
            generate:
                - new('test', number=1000)

            f1(a):
                - return a + 1
            f2(a):
                - r: a + 1
                - return r

            test_issue:
                # works
                - y: id[0]
                - z: y + f2(1)
                - z: id[0] + f1(1)
                # fails
                - z: id[0] + f2(1)

simulation:
    processes:
        - test: [generate, test_issue]
    input:
        method: void
        file: none
    output:
        file: output.h5
    start_period: 2015
    periods: 1