Avoid crashing in SentryCoreDataTracker (#3152)

Users can pass in a `nil` error parameter when calling Core Data methods like `save:` and `executeFetchRequest:`. We were incorrectly handling that nil error parameter and trying to dereference it inside SENTRY_LOG_DEBUG calls. This commit fixes that.

Fixes GH-3151

Author: bjhomer

Sources/Sentry/SentryCoreDataTracker.m

@@ -67,7 +67,7 @@ - (NSArray *)managedObjectContext:(NSManagedObjectContext *)context
             finishWithStatus:result == nil ? kSentrySpanStatusInternalError : kSentrySpanStatusOk];
 
         SENTRY_LOG_DEBUG(@"SentryCoreDataTracker automatically finished span with status: %@",
-            error == nil ? @"ok" : @"error");
+            result == nil ? @"error" : @"ok");
     }
 
     return result;
@@ -109,7 +109,7 @@ - (BOOL)managedObjectContext:(NSManagedObjectContext *)context
         [fetchSpan finishWithStatus:result ? kSentrySpanStatusOk : kSentrySpanStatusInternalError];
 
         SENTRY_LOG_DEBUG(@"SentryCoreDataTracker automatically finished span with status: %@",
-            *error == nil ? @"ok" : @"error");
+            result ? @"ok" : @"error");
     }
 
     return result;