Fix logic around warning about keyframe interval being larger than max image buffer count.

src/zm_packetqueue.cpp

@@ -308,8 +308,10 @@ void PacketQueue::clearPackets(const std::shared_ptr<ZMPacket> &add_packet) {
     } // end while
   }  // end if first packet not locked
 
-  if (keyframe_interval > pre_event_video_packet_count) {
-    Warning("Max Image Buffer setting is too low! Needs to be great than keyframe interval. Keyframe interval is at least %d", keyframe_interval);
+  if ((keyframe_interval == 1) and max_video_packet_count) {
+    Warning("Did not find a second keyframe in the packet queue. It may be that"
+        " the Max Image Buffer setting is lower than the keyframe interval. We"
+        " need it to be greater than the keyframe interval.");
   }
   Debug(1, "Resulting it pointing at latest packet? %d, next front points to begin? %d, Keyframe interval %d",
       ( *it == add_packet ),