title: FMDBBlockSQLiteCallBackFunction Crash in app that's not using makeFunctionNamed
body: <p>I'm working on an app that's in the app store, which uses <code>FMDB</code> for interacting with its sqlite database. We've received some crash reports with stack traces like this:</p>
  
  <pre><code>Thread : Crashed: NSOperationQueue 0x170239c20 :: NSOperation 0x17024d7d0 (QOS: LEGACY)
  0  libobjc.A.dylib                0x000000019701c0b4 objc_retain + 20
  1  MyApp                          0x00000001002bdff4 FMDBBlockSQLiteCallBackFunction
  2  MyApp                          0x00000001002bdb1c FMDBBlockSQLiteCallBackFunction
  3  MyApp                          0x00000001002b66b4 FMDBBlockSQLiteCallBackFunction
  4  MyApp                          0x00000001002980fc FMDBBlockSQLiteCallBackFunction
  5  MyApp                          0x000000010029f20c FMDBBlockSQLiteCallBackFunction
  6  CFNetwork                      0x00000001851475a4 __49-[__NSCFLocalSessionTask _task_onqueue_didFinish]_block_invoke + 300
  7  Foundation                     0x00000001866bf1c4 __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 16
  8  Foundation                     0x0000000186610604 -[NSBlockOperation main] + 96
  9  Foundation                     0x00000001866001cc -[__NSOperationInternal _start:] + 636
  10 Foundation                     0x00000001866c1f28 __NSOQSchedule_f + 228
  11 libdispatch.dylib              0x0000000197655954 _dispatch_client_callout + 16
  12 libdispatch.dylib              0x00000001976600a4 _dispatch_queue_drain + 1448
  13 libdispatch.dylib              0x0000000197658a5c _dispatch_queue_invoke + 132
  14 libdispatch.dylib              0x0000000197662318 _dispatch_root_queue_drain + 720
  15 libdispatch.dylib              0x0000000197663c4c _dispatch_worker_thread3 + 108
  16 libsystem_pthread.dylib        0x000000019783522c _pthread_wqthread + 816
  </code></pre>
  
  <p>However, from reading the <code>FMDB</code> code it looks like <code>FMDBBlockSQLiteCallBackFunction</code> is only called as the callback for <code>SQLite</code> functions created using <code>FMDatabase</code>'s <code>makeFunctionNamed:maximumArguments:withBlock:</code> method, which we're not using at all.</p>
  
  <p>Any ideas what could be causing crashes like this?</p>