Re-enabling J/P/Q button unexpectedly scrolls to near top of buffer

[phuzion]

Summary:

When re-enabling J/P/Q's in a buffer after previously hiding J/P/Q's, the chat log scrolls almost all the way to the top of whatever is loaded into memory.

Steps to reproduce:

• Install iQuassel 1.9.0 or later, connect to a core
• Scroll back in chat history to have a few pages worth of history in memory (least recent)
• Scroll to the bottom of the chat history (most recent)
• Tap J/P/Q to hide joins, parts and quits in the current buffer.
• If there is not a full page of chat history on the page, scroll back to get more (least recent)
• Scroll to the bottom of the chat history (most recent)
• Tap J/P/Q again to unhide joins, parts and quits in the current buffer.

Expected behavior:

Joins, parts and quits will appear and disappear without affecting the user's scroll position in the buffer

Actual behavior:

iQuassel unexpectedly scrolls to near the top of the buffer loaded into memory, losing the user's place in the chat history.

[guruz]

iquassel/quassel-for-ios/quassel-for-ios/vcs/BufferViewController.m

Line 705 in a39f570

// FIXME: This is annoying but not doing anything is annoying too