Deleting a damaged graph can sometimes led to removal of valid graphs too

[TheWitness]

Describe the bug

In certain cases, where for example, you database has been corrupted due to a bug, it is possible to create a graph with a graph id of 0. When you go to delete that corrupt graph, you also delete all your Graph Templates.

To Reproduce

Create a graph manually with a id in the graph_local table of 0, then delete it.

Expected behavior

Cacti should remove the local graph id, but not any templates.