Catch json decode error

scripts/knotctl

@@ -313,6 +313,10 @@ def main() -> int:
     except KeyError:
         output(response.json())
         return 1
+    except json.JSONDecodeError:
+        output(
+            error("Could not decode api response as JSON", "Could not decode"))
+        return 1
     headers = {"Authorization": "Bearer {}".format(token)}
 
     # Route based on command