Apply nl_func_var_def_blk only to first block

[xeyownt]

Hello,

This is a small fix that addresses nl_func_var_def_blk applying to all var block in a function, not only the top one.

Consider the following example:

void foo(void)
{
    int a;
    bar();
    int b;
    baz();
}

Say you have nl_func_var_def_blk=1, this would give before this fix:

void foo(void)
{
    int a;
                 // <-- good
    bar();
    int b;
                 // <-- bad!
    baz();
}

After this fix, you get the correct:

void foo(void)
{
    int a;

    bar();
    int b;
    baz();
}

This is not the final fix though.

Ideally, if var block is preceded by any other (non-var) block,
nl_func_var_def_blk should not apply as well (because not func top).

For instance, you would still get

void foo(void)
{
    bat();
    int a;
                       // <-- space still inserted here, but a is no longer function top
    bar();
    int b;
    baz();
}

[gmaurel]

The idea is OK, but you need to solve the problems shown at:
https://github.com/xeyownt/uncrustify/runs/3086051478?check_suite_focus=true
Add at least one test data to show how it works