Filter out falsy nodes in blocks

[motiz88]

Fixes #84 and adds a regression test. This is perhaps a crude fix, as I chose not to hunt down the specific null-producing cases in e.g. parser/if.js, but rather to remove them after the fact in the Block constructor.

[coveralls]

Coverage remained the same at 94.401% when pulling 1e18f48 on motiz88:fix-84 into a99ae87 on glayzzle:master.

[ichiriac]

Hi @motiz88,

Thanks for the fix. I've digged into the issue, it's caused by this code : https://github.com/glayzzle/php-parser/blob/master/src/parser/statement.js#L317

It can also be reproduced by this code :

<?php if (true): ; ; ?>
<?php endif; ?>

The actual fix works on every case, but may slow down a bit the AST building process. I'm looking at a more early filtering solution.

On the other hand, the bracket { ... } form does not have the problem because the falsy values are filtered here : https://github.com/glayzzle/php-parser/blob/master/src/parser/statement.js#L83

I've also found a helper here https://github.com/glayzzle/php-parser/blob/master/src/parser/utils.js#L15 used on loops (could be fixed and used with multiple tokens)

Do you want to digg more ?

If you don't have the time I can merge the fix and continue to correct accordingly.