[property] avoid receiver buffer overflow in some cases

Logical error: receiver byte array resized w/o taking cap into
accout. Do it properly and check is it ok when reading. Also do not
allow to grow buffer indefinitely.

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Merge pull request #8 from nemomobile/fix-buffer-overflow

[property] avoid receiver buffer overflow in some cases