Fix combined error and completion handling (#11225)

Author: paulb777

FirebaseAuth/Sources/Auth/FIRAuth.m

@@ -1537,11 +1537,11 @@ - (void)revokeTokenWithAuthorizationCode:(NSString *)authorizationCode
                               completion:(nullable void (^)(NSError *_Nullable error))completion {
   [self.currentUser
       getIDTokenWithCompletion:^(NSString *_Nullable idToken, NSError *_Nullable error) {
-        if (completion) {
-          if (error) {
+        if (error) {
+          if (completion) {
             completion(error);
-            return;
           }
+          return;
         }
         FIRRevokeTokenRequest *request =
             [[FIRRevokeTokenRequest alloc] initWithToken:authorizationCode
@@ -1703,8 +1703,7 @@ - (void)signInWithPhoneCredential:(FIRPhoneAuthCredential *)credential
     @param completion A block which is invoked when the custom token sign in request completes.
  */
 - (void)internalSignInAndRetrieveDataWithCustomToken:(NSString *)token
-                                          completion:
-                                              (nullable FIRAuthDataResultCallback)completion {
+                                          completion:(FIRAuthDataResultCallback)completion {
   FIRVerifyCustomTokenRequest *request =
       [[FIRVerifyCustomTokenRequest alloc] initWithToken:token
                                     requestConfiguration:_requestConfiguration];
@@ -1713,18 +1712,16 @@ - (void)internalSignInAndRetrieveDataWithCustomToken:(NSString *)token
                callback:^(FIRVerifyCustomTokenResponse *_Nullable response,
                           NSError *_Nullable error) {
                  if (error) {
-                   if (completion) {
-                     completion(nil, error);
-                     return;
-                   }
+                   completion(nil, error);
+                   return;
                  }
                  [self completeSignInWithAccessToken:response.IDToken
                            accessTokenExpirationDate:response.approximateExpirationDate
                                         refreshToken:response.refreshToken
                                            anonymous:NO
                                             callback:^(FIRUser *_Nullable user,
                                                        NSError *_Nullable error) {
-                                              if (error && completion) {
+                                              if (error) {
                                                 completion(nil, error);
                                                 return;
                                               }
@@ -1739,9 +1736,7 @@ - (void)internalSignInAndRetrieveDataWithCustomToken:(NSString *)token
                                                                    initWithUser:user
                                                              additionalUserInfo:additonalUserInfo]
                                                        : nil;
-                                              if (completion) {
-                                                completion(result, error);
-                                              }
+                                              completion(result, error);
                                             }];
                }];
 }