Fix getCurrentPosition

Summary:
Instantiates the _pendingRequests array before trying to add to it. As it currently stands, we try to add the pending request before the array is created. getCurrentPosition always fails on the first try.
Closes #4764

Reviewed By: svcscm

Differential Revision: D2764751

Pulled By: androidtrunkagent

fb-gh-sync-id: 411a03ff16d40725d8cc0909607632045eb5a27b

Libraries/Geolocation/RCTLocationObserver.m

@@ -130,7 +130,6 @@ - (void)beginLocationUpdates
     _locationManager = [CLLocationManager new];
     _locationManager.distanceFilter = RCT_DEFAULT_LOCATION_ACCURACY;
     _locationManager.delegate = self;
-    _pendingRequests = [NSMutableArray new];
   }
 
   // Request location access permission
@@ -234,6 +233,9 @@ - (void)timeout:(NSTimer *)timer
                                                         selector:@selector(timeout:)
                                                         userInfo:request
                                                          repeats:NO];
+  if (!_pendingRequests) {
+    _pendingRequests = [NSMutableArray new];
+  }
   [_pendingRequests addObject:request];
 
   // Configure location manager and begin updating location