fix(langgraph): Fix validation and drawing for edgeless graphs (#723) #1990

Job	Run time
Build	1m 45s
Check linting	1m 44s
check-readmes-synced	3s
Check formatting	1m 21s
Unit Tests (ubuntu-latest, 18.x)	1m 27s
Validate Deno and Node dependencies in sync	4s
validate-new-notebooks	4s
Unit Tests (ubuntu-latest, 20.x)	1m 22s
Unit Tests (ubuntu-latest, 22.4.1)	2m 8s
Unit Tests (windows-latest, 22.4.1)	3m 55s
Unit Tests (macos-latest, 22.4.1)	1m 39s
	15m 32s

Provide feedback