Remove panics from service's create_inherent_data_providers function (

#126)

wow, we really can handle these errors gracefully.

node/src/service.rs

@@ -244,14 +244,12 @@ pub fn new_full(config: Configuration) -> Result<TaskManager, ServiceError> {
                 block_import,
                 proposer_factory,
                 create_inherent_data_providers: move |parent_hash, ()| {
-                    let parent_block = client_for_cidp
-                        .clone()
-                        .block(parent_hash)
-                        .expect("Block backend should not error.")
-                        .expect("Parent block should be found in database for authoring to work.")
-                        .block;
+                    let maybe_parent_block = client_for_cidp.clone().block(parent_hash);
 
                     async move {
+                        let parent_block = maybe_parent_block?
+                            .ok_or(sp_blockchain::Error::UnknownBlock(parent_hash.to_string()))?
+                            .block;
                         let parent_idp =
                             tuxedo_core::inherents::ParentBlockInherentDataProvider(parent_block);
                         let timestamp = sp_timestamp::InherentDataProvider::from_system_time();