fix: Crash when user feedback block is nil

Author: noahsmartin

Sources/Sentry/SentryOptions.m

@@ -395,7 +395,9 @@ - (void)setConfigureUserFeedback:(SentryUserFeedbackConfigurationBlock)configure
     SentryUserFeedbackConfiguration *userFeedbackConfiguration =
         [[SentryUserFeedbackConfiguration alloc] init];
     self.userFeedbackConfiguration = userFeedbackConfiguration;
-    configureUserFeedback(userFeedbackConfiguration);
+    if (userFeedbackConfiguration) {
+        configureUserFeedback(userFeedbackConfiguration);
+    }
 }
 #endif // TARGET_OS_IOS && SENTRY_HAS_UIKIT