Avoid panicking when a native library doesn't exist

src/native_loader.rs

@@ -70,8 +70,8 @@ pub fn process_transaction(keyed_accounts: &mut [KeyedAccount], tx_data: &[u8])
         trace!("Call native {:?}", name);
         let path = create_path(&name);
         // TODO linux tls bug can cause crash on dlclose(), workaround by never unloading
-        let library = Library::open(Some(path), libc::RTLD_NODELETE | libc::RTLD_NOW).unwrap();
-        unsafe {
+        match Library::open(Some(&path), libc::RTLD_NODELETE | libc::RTLD_NOW) {
+            Ok(library) => unsafe {
                 let entrypoint: Symbol<Entrypoint> = match library.get(ENTRYPOINT.as_bytes()) {
                     Ok(s) => s,
                     Err(e) => {
@@ -80,6 +80,11 @@ pub fn process_transaction(keyed_accounts: &mut [KeyedAccount], tx_data: &[u8])
                     }
                 };
                 return entrypoint(&mut keyed_accounts[1..], tx_data);
+            },
+            Err(e) => {
+                warn!("Unable to load: {:?}", e);
+                return false;
+            }
         }
     } else if let Ok(instruction) = deserialize(tx_data) {
         match instruction {