Fix build warnings

Signed-off-by: Terry Yiu <git@tyiu.xyz>
Reviewed-by: William Casarin <jb55@jb55.com>

damus/Models/HomeModel.swift

@@ -154,7 +154,7 @@ class HomeModel {
                 print("nwc: \(resp.req_id) not found in the postbox, nothing to remove [\(relay)]")
             }
             
-            guard let err = resp.response.error else {
+            guard resp.response.error != nil else {
                 print("nwc success: \(resp.response.result.debugDescription) [\(relay)]")
                 nwc_success(state: self.damus_state, resp: resp)
                 return