fix crash in status items filter

App will crash (or no status bar icon shown) if status filter is enabled.
Fixes bug in commit: fbe323c87d49

```
2014/11/14 11:03:10.989 Trailer[1976]: *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse the format string "pullRequest == %@ and (not (%@))"'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff8a96525c __exceptionPreprocess + 172
	1   libobjc.A.dylib                     0x00007fff8c67ae75 objc_exception_throw + 43
	2   Foundation                          0x00007fff942394b4 _qfqp2_performParsing + 338
	3   Foundation                          0x00007fff942392f6 +[NSPredicate predicateWithFormat:arguments:] + 46
	4   Foundation                          0x00007fff942392b0 +[NSPredicate predicateWithFormat:] + 142
	5   Trailer                             0x00000001042ceadb Trailer + 117467
	6   Trailer                             0x00000001042cf8ee Trailer + 121070
	7   Trailer                             0x00000001042d85b2 Trailer + 157106
	8   Trailer                             0x00000001042dea15 Trailer + 182805
	9   Trailer                             0x00000001042de1d8 Trailer + 180696
	10  Trailer                             0x00000001042de57a Trailer + 181626
	11  Trailer                             0x00000001042bacc8 Trailer + 36040
	12  Trailer                             0x00000001042c118f Trailer + 61839
	13  libdispatch.dylib                   0x00007fff8a7a81bb _dispatch_call_block_and_release + 12
	14  libdispatch.dylib                   0x00007fff8a7a528d _dispatch_client_callout + 8
	15  libdispatch.dylib                   0x00007fff8a7acef0 _dispatch_main_queue_callback_4CF + 333
	16  CoreFoundation                      0x00007fff8a8cc4f9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
	17  CoreFoundation                      0x00007fff8a887714 __CFRunLoopRun + 1636
	18  CoreFoundation                      0x00007fff8a886e75 CFRunLoopRunSpecific + 309
	19  HIToolbox                           0x00007fff8fbbaa0d RunCurrentEventLoopInMode + 226
	20  HIToolbox                           0x00007fff8fbba7b7 ReceiveNextEventCommon + 479
	21  HIToolbox                           0x00007fff8fbba5bc _BlockUntilNextEventMatchingListInModeWithFilter + 65
	22  AppKit                              0x00007fff8d19124e _DPSNextEvent + 1434
	23  AppKit                              0x00007fff8d19089b -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 122
	24  AppKit                              0x00007fff8d18499c -[NSApplication run] + 553
	25  AppKit                              0x00007fff8d16f783 NSApplicationMain + 940
	26  libdyld.dylib                       0x00007fff8ced95fd start + 1
)
```

Thanks for great app!