provide default init values for JSQMessagesCollectionViewLayoutAttributes to prevent assertion. fix #1338

Author: jessesquires

JSQMessagesViewController/Layout/JSQMessagesCollectionViewFlowLayout.m

@@ -319,7 +319,7 @@ - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
 
 - (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
 {
-    JSQMessagesCollectionViewLayoutAttributes *customAttributes = (JSQMessagesCollectionViewLayoutAttributes *)[super layoutAttributesForItemAtIndexPath:indexPath];
+    JSQMessagesCollectionViewLayoutAttributes *customAttributes = (JSQMessagesCollectionViewLayoutAttributes *)[[super layoutAttributesForItemAtIndexPath:indexPath] copy];
 
     if (customAttributes.representedElementCategory == UICollectionElementCategoryCell) {
         [self jsq_configureMessageCellLayoutAttributes:customAttributes];

JSQMessagesViewController/Layout/JSQMessagesCollectionViewLayoutAttributes.m

@@ -20,6 +20,17 @@
 
 @implementation JSQMessagesCollectionViewLayoutAttributes
 
+#pragma mark - Init
+
+- (instancetype)init {
+    self = [super init];
+    if (self) {
+        _messageBubbleFont = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
+        _messageBubbleContainerViewWidth = 320.0f;
+    }
+    return self;
+}
+
 #pragma mark - Setters
 
 - (void)setMessageBubbleFont:(UIFont *)messageBubbleFont