start readtimer whenever we become active

// FREEBIE

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -317,6 +317,10 @@ typedef enum : NSUInteger {
                                              selector:@selector(applicationWillResignActive:)
                                                  name:OWSApplicationWillResignActiveNotification
                                                object:nil];
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(applicationDidBecomeActive:)
+                                                 name:OWSApplicationDidBecomeActiveNotification
+                                               object:nil];
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(cancelReadTimer)
                                                  name:OWSApplicationDidEnterBackgroundNotification
@@ -604,6 +608,11 @@ typedef enum : NSUInteger {
     [self dismissPresentedViewControllerIfNecessary];
 }
 
+- (void)applicationDidBecomeActive:(NSNotification *)notification
+{
+    [self startReadTimer];
+}
+
 - (void)dismissPresentedViewControllerIfNecessary
 {
     UIViewController *_Nullable presentedViewController = self.presentedViewController;