Fix crash when converting topology with broken link

Fix #845

gns3server/controller/topology.py

@@ -310,20 +310,23 @@ def _convert_1_3_later(topo, topo_path):
 
     # Create links
     for old_link in topo.get("links", []):
-        nodes = []
-        source_node = {
-            "adapter_number": ports[old_link["source_port_id"]].get("adapter_number", 0),
-            "port_number": ports[old_link["source_port_id"]].get("port_number", 0),
-            "node_id": node_id_to_node_uuid[old_link["source_node_id"]]
-        }
-        nodes.append(source_node)
+        try:
+            nodes = []
+            source_node = {
+                "adapter_number": ports[old_link["source_port_id"]].get("adapter_number", 0),
+                "port_number": ports[old_link["source_port_id"]].get("port_number", 0),
+                "node_id": node_id_to_node_uuid[old_link["source_node_id"]]
+            }
+            nodes.append(source_node)
 
-        destination_node = {
-            "adapter_number": ports[old_link["destination_port_id"]].get("adapter_number", 0),
-            "port_number": ports[old_link["destination_port_id"]].get("port_number", 0),
-            "node_id": node_id_to_node_uuid[old_link["destination_node_id"]]
-        }
-        nodes.append(destination_node)
+            destination_node = {
+                "adapter_number": ports[old_link["destination_port_id"]].get("adapter_number", 0),
+                "port_number": ports[old_link["destination_port_id"]].get("port_number", 0),
+                "node_id": node_id_to_node_uuid[old_link["destination_node_id"]]
+            }
+            nodes.append(destination_node)
+        except KeyError:
+            continue
 
         link = {
             "link_id": str(uuid.uuid4()),