viewer: fixed issue with reverse playback

app/widget/viewer/viewerdisplay.cpp

@@ -66,6 +66,7 @@ ViewerDisplayWidget::ViewerDisplayWidget(QWidget *parent) :
   show_fps_(false),
   frames_skipped_(0),
   show_widget_background_(false),
+  playback_speed_(0),
   push_mode_(kPushNull),
   add_band_(nullptr),
   queue_starved_(false)
@@ -882,6 +883,7 @@ void ViewerDisplayWidget::RequestStartEditingText()
 void ViewerDisplayWidget::Play(const int64_t &start_timestamp, const int &playback_speed, const rational &timebase)
 {
   playback_timebase_ = timebase;
+  playback_speed_ = playback_speed;
 
   timer_.Start(start_timestamp, playback_speed, timebase.toDouble());
 
@@ -924,7 +926,7 @@ void ViewerDisplayWidget::UpdateFromQueue()
         }
         return;
 
-      } else if (pf.timestamp > time) {
+      } else if ((pf.timestamp > time) == (playback_speed_ > 0)) {
 
         // The next frame in the queue is too new, so just do a regular update. Either the
         // frame we want will arrive in time, or we'll just have to skip it.

app/widget/viewer/viewerdisplay.h

@@ -360,6 +360,8 @@ private:
 
   QVariant load_frame_;
 
+  int playback_speed_;
+
   enum PushMode {
     /// New frame to push to internal texture
     kPushFrame,

app/widget/viewer/viewerqueue.h

@@ -41,7 +41,7 @@ public:
     if (this->empty() || (this->back().timestamp < f.timestamp) == (playback_speed > 0)) {
       this->push_back(f);
     } else {
-      for (iterator i=this->begin(); i!=this->end(); i++) {
+      for (auto i=this->begin(); i!=this->end(); i++) {
         if ((i->timestamp > f.timestamp) == (playback_speed > 0)) {
           this->insert(i, f);
           break;