fix(node): regression in input check since 1.6.2

[gierschv]

Mailchecker.is_valid(undefined) should return false, not crash (since f5f5b36);

By the way, thanks for the breaking change in f5f5b36 released in patch release 1.6.2 (MailChecker.is_valid vs MailChecker).

Cheers,
Vincent

[FGRibreau]

+1, note that 1.6.2 was unpublished soon after its release:

   [ '0.1.0',
     '0.1.1',
     '0.1.2',
     '0.1.3',
     '0.1.4',
     '0.1.5',
     '0.1.7',
     '0.1.8',
     '0.1.10',
     '0.1.11',
     '0.2.0',
     '1.0.0',
     '1.1.0',
     '1.1.1',
     '1.2.0',
     '1.3.0',
     '1.3.1',
     '1.4.0',
     '1.5.0',
     '1.5.1',
     '1.5.2',
     '1.6.0',
     '1.6.1',
     '2.0.0',
     '2.0.1' ],

[FGRibreau]

@gierschv mailchecker v3.0.0 released