fix last two warnings

src/dc_job.rs

@@ -110,7 +110,7 @@ unsafe fn dc_job_perform(context: &Context, thread: libc::c_int, probe_network:
         },
     );
     match jobs {
-        Ok(ref res) => {}
+        Ok(ref _res) => {}
         Err(ref err) => {
             info!(context, 0, "query failed: {:?}", err);
         }

src/dc_msg.rs

@@ -487,10 +487,7 @@ pub fn dc_msg_load_from_db<'a>(msg: *mut dc_msg_t<'a>, context: &'a Context, id:
         }
     );
 
-    match res {
-        Ok(_) => true,
-        Err(err) => false,
-    }
+    res.is_ok()
 }
 
 pub unsafe fn dc_get_mime_headers(context: &Context, msg_id: uint32_t) -> *mut libc::c_char {