Parses the first vCard entry in InputStream and lets registered {@link VCardInterpreter}
instances handle callbacks.
This method finishes itself when the first entry ended.
Note that, registered {@link VCardInterpreter} may still see multiple
{@link VCardInterpreter#onEntryStarted()} / {@link VCardInterpreter#onEntryEnded()} calls
even with this method.
This happens when the first entry contains nested vCards, which is allowed in vCard 2.1.
See the following example.
BEGIN:VCARD
N:a
BEGIN:VCARD
N:b
END:VCARD
END:VCARD
With this vCard, registered interpreters will grab two
{@link VCardInterpreter#onEntryStarted()} and {@link VCardInterpreter#onEntryEnded()}
calls. Callers should handle the situation by themselves.