[JSQMVC] Fix crash on delete when under load.

Hack to fix https://github.com/jessesquires/JSQMessagesViewController/issues/1885

This doesn't happen often, but is reproducible under simulated message
churn (~50 insert/update/deletes randomly spaced over 10 seconds).

During performBatchUpdates, the collectionViewLayout can call
layoutAttributesForElementsInRect which can reference the just-deleted
item's
view. (The view presumably hasn't been deleted yet, but will be by the
time
performBatchUpdates is complete).

It's opaque how layoutAttributesForElementsInRect get's it's list of
views. I
can only speculate how this works based on debugging, but it seems that
the
CollectionFlowLayout keeps an internal list of item frames, which when
crashing
still contain items corresponding to the to-be-deleted items.

In any case, it seems like a bug that JSQMVC would ever attempt to get
layoutAttributes for an item which doesn't exist in the datasource.

Podfile

@@ -11,7 +11,8 @@ target 'Signal' do
     pod 'SCWaveformView',             '~> 1.0'
     pod 'ZXingObjC'
     pod 'DJWActionSheet'
-    pod 'JSQMessagesViewController'
+    #pod 'JSQMessagesViewController'
+    pod 'JSQMessagesViewController', git: 'https://github.com/WhisperSystems/JSQMessagesViewController.git', branch: 'fix-intermittent-crash-on-delete'
     target 'SignalTests' do
         inherit! :search_paths
     end

Podfile.lock

@@ -118,7 +118,7 @@ PODS:
 DEPENDENCIES:
   - DJWActionSheet
   - FFCircularProgressView (~> 0.5)
-  - JSQMessagesViewController
+  - JSQMessagesViewController (from `https://github.com/WhisperSystems/JSQMessagesViewController.git`, branch `fix-intermittent-crash-on-delete`)
   - OpenSSL
   - PastelogKit (~> 1.3)
   - SCWaveformView (~> 1.0)
@@ -127,12 +127,18 @@ DEPENDENCIES:
   - ZXingObjC
 
 EXTERNAL SOURCES:
+  JSQMessagesViewController:
+    :branch: fix-intermittent-crash-on-delete
+    :git: https://github.com/WhisperSystems/JSQMessagesViewController.git
   SignalServiceKit:
     :git: https://github.com/WhisperSystems/SignalServiceKit.git
   SocketRocket:
     :git: https://github.com/facebook/SocketRocket.git
 
 CHECKOUT OPTIONS:
+  JSQMessagesViewController:
+    :commit: 03cde781234ade464dd26914d87e6e95afde1119
+    :git: https://github.com/WhisperSystems/JSQMessagesViewController.git
   SignalServiceKit:
     :commit: 9c426e0a4b3b29afe8becbe96c5cf458681489de
     :git: https://github.com/WhisperSystems/SignalServiceKit.git
@@ -166,6 +172,6 @@ SPEC CHECKSUMS:
   YapDatabase: b1e43555a34a5298e23a045be96817a5ef0da58f
   ZXingObjC: bf15b3814f7a105b6d99f47da2333c93a063650a
 
-PODFILE CHECKSUM: 93ccdbbb243044904d772ee53e00154890a9f82f
+PODFILE CHECKSUM: 0e619684d8a5fa1ddbab78c0821d74af558fd7df
 
 COCOAPODS: 1.0.1