Add workaround for bug in iOS 11.1 beta around hit area of custom back buttons.

// FREEBIE

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -1106,6 +1106,7 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
 - (void)createBackButton
 {
     UIBarButtonItem *backItem = [self createOWSBackButton];
+    if (backItem.customView) {
         // This method gets called multiple times, so it's important we re-layout the unread badge
         // with respect to the new backItem.
         [backItem.customView addSubview:_backButtonUnreadCountView];
@@ -1127,6 +1128,7 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
 
         // Initialize newly created unread count badge to accurately reflect the current unread count.
         [self updateBackButtonUnreadCount];
+    }
 
     self.navigationItem.leftBarButtonItem = backItem;
 }

Signal/src/util/UIViewController+OWS.m

@@ -53,6 +53,22 @@ NS_ASSUME_NONNULL_BEGIN
         = CGRectMake(0, 0, backImage.size.width + kExtraRightPadding, backImage.size.height + kExtraHeightPadding);
     backButton.frame = buttonFrame;
 
+    if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(11, 1)) {
+        // In iOS 11.1 beta, the hot area of custom bar button items is _only_
+        // the bounds of the custom view, making them very hard to hit.
+        //
+        // TODO: Remove this hack if the bug is fixed in iOS 11.1 by the time
+        //       it goes to production (or in a later release),
+        //       since it has two negative side effects: 1) the layout of the
+        //       back button isn't consistent with the iOS default back buttons
+        //       2) we can't add the unread count badge to the back button
+        //       with this hack.
+        return [[UIBarButtonItem alloc] initWithImage:backImage
+                                                style:UIBarButtonItemStylePlain
+                                               target:target
+                                               action:selector];
+    }
+
     UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
     backItem.width = buttonFrame.size.width;