Fix layout of Canvas elements when there isn't enough space on the current page.

src/libprs500/gui2/lrf_renderer/document.py

@@ -105,6 +105,9 @@ class _Canvas(QGraphicsRectItem):
             self.layout_canvas(block, x, y)
             
     def layout_canvas(self, canvas, x, y):
+        if canvas.max_y + y > self.max_y:
+            self.is_full = True
+            return 
         canvas.setParentItem(self)
         canvas.setPos(x, y)
         canvas.has_content = False