Better handling of FITS loading error

imageringlist.cpp

@@ -85,6 +85,11 @@ void Image::clearThumbnail()
     m_thumbnail.reset();
 }
 
+bool Image::isLoading() const
+{
+    return m_loading;
+}
+
 void Image::imageLoaded(std::shared_ptr<RawImage> rawImage, ImageInfoData info)
 {
     m_loading = false;
@@ -200,7 +205,7 @@ void ImageRingList::increment()
     if(m_images.size())
     {
         //don't increment if current image was not loaded yet
-        if(!(*m_currImage)->rawImage())
+        if((*m_currImage)->isLoading())
             return;
 
         (*m_firstImage)->release();
@@ -216,6 +221,10 @@ void ImageRingList::decrement()
 {
     if(m_images.size())
     {
+        //don't decrement if current image was not loaded yet
+        if((*m_currImage)->isLoading())
+            return;
+
         (*m_lastImage)->release();
         m_firstImage = decrement(m_firstImage);
         m_currImage = decrement(m_currImage);