Defensively disables allocation of anything outside of visible lines.

Outputs/ScanTargets/BufferingScanTarget.cpp

@@ -249,6 +249,9 @@ void BufferingScanTarget::announce(Event event, bool is_visible, const Outputs::
 			write_pointers_ = submit_pointers_.load(std::memory_order::memory_order_relaxed);
 			frame_is_complete_ &= !allocation_has_failed_;
 		}
+
+		// Don't permit anything to be allocated on invisible areas.
+		allocation_has_failed_ = true;
 	}
 }