addTitle() buggy (and solution).

[Muqsit]

Issue description

When sending title to player after you've already sent them a title some time ago, the title glitches.
The following could be the result:

• The subtitle, if set, would still not be shown.
• The player would receive a previously sent subtitle/title.

Steps to reproduce the issue

1. Send the player a title with a subtitle using Player::addTitle("", "").
2. Wait a few seconds.
3. Send the player another title with a subtitle (make the text different from the first one to spot differences).
4. Watch how they glitch.

OS and versions

• PocketMine-MP: 7c66af5
• PHP: 7.0.17
• Server OS: Ubuntu 14.04 64-bit
• Game version: Win10

Crashdump, backtrace or other files

-=-

[moskadev]

Thanks Max x)

[dktapps]

Please create a pull request if you know how to fix the issue.

[Muqsit]

This has been fixed in api3/network. Closing..

[dktapps]

I meant to squash-merge that PR, but my browser was acting up. There are two commits on the branch head, yours (319763d) and the merge commit (40775f5).