graph: Fix converting bytes values to Option<H256>

The other option would be to use `H256::from_slice` but that panics
if the slice length isn't 32 bytes. It seems better to catch invalid
hashes rather than crashing the entire node.

Author: Jannis

graph/src/data/store/mod.rs

@@ -396,7 +396,7 @@ impl TryFrom<Value> for Option<H256> {
         match value {
             Value::Bytes(bytes) => {
                 let hex = format!("{}", bytes);
-                Ok(Some(H256::from_str(hex.as_str())?))
+                Ok(Some(H256::from_str(hex.as_str().trim_start_matches("0x"))?))
             }
             Value::String(s) => Ok(Some(H256::from_str(s.as_str())?)),
             Value::Null => Ok(None),