iOS: Fix problem where slider returned to original position. (callstack#235)

If the slide was quick, the new tap gesture recognizer would be
invoked and cause the slider to return to its original position
(ignoring the slide).

Author: MarkCSmith

src/ios/RNCSliderManager.m

@@ -11,9 +11,11 @@
 #import <React/RCTEventDispatcher.h>
 #import "RNCSlider.h"
 #import <React/UIView+React.h>
-#import "os/log.h"
 
 @implementation RNCSliderManager
+{
+  BOOL _isSliding;
+}
 
 RCT_EXPORT_MODULE()
 
@@ -38,6 +40,11 @@ - (UIView *)view
 }
 
 - (void)tapHandler:(UITapGestureRecognizer *)gesture {
+  // Ignore this tap if in the middle of a slide.
+  if (_isSliding) {
+    return;
+  }
+
   // Bail out if the source view of the gesture isn't an RNCSlider.
   if ([gesture.view class] != [RNCSlider class]) {
     return;
@@ -121,11 +128,13 @@ - (void)sliderValueChanged:(RNCSlider *)sender
 - (void)sliderTouchStart:(RNCSlider *)sender
 {
   RNCSendSliderEvent(sender, NO, YES);
+  _isSliding = YES;
 }
 
 - (void)sliderTouchEnd:(RNCSlider *)sender
 {
   RNCSendSliderEvent(sender, NO, NO);
+  _isSliding = NO;
 }
 
 RCT_EXPORT_VIEW_PROPERTY(value, float);