Block 0 is valid in queries (#8891)

Early exit for block nr 0 leads to spurious error about pruning: `…your node is running with state pruning…`.

Fixes #7547, #8762

ethcore/src/client/client.rs

@@ -1047,7 +1047,8 @@ impl Client {
 	/// Otherwise, this can fail (but may not) if the DB prunes state.
 	pub fn state_at_beginning(&self, id: BlockId) -> Option<State<StateDB>> {
 		match self.block_number(id) {
-			None | Some(0) => None,
+			None => None,
+			Some(0) => self.state_at(id),
 			Some(n) => self.state_at(BlockId::Number(n - 1)),
 		}
 	}