fix some crashes, mostly related to network requests (#6187)

src/messages/Image.cpp

@@ -282,6 +282,15 @@ Image::~Image()
         return;
     }
 
+    if (isAppAboutToQuit())
+    {
+        if (this->frames_)
+        {
+            std::ignore = this->frames_.release();
+        }
+        return;
+    }
+
     // Ensure the destructor for our frames is called in the GUI thread
     // If the Image destructor is called outside of the GUI thread, move the
     // ownership of the frames to the GUI thread, otherwise the frames will be
@@ -488,6 +497,8 @@ void Image::actuallyLoad()
                 return;
             }
 
+            assert(!isAppAboutToQuit());
+
             QBuffer buffer;
             buffer.setData(result.getData());
             QImageReader reader(&buffer);