Prevent UITextView from updating contentOffset while deallocating (#915)

* Prevent UITextView from updating contentOffset while deallocating

* Add comment on the flag point to the issue

Source/TextKit/ASTextKitComponents.mm

@@ -20,7 +20,10 @@
 
 #import <tgmath.h>
 
-@interface ASTextKitComponentsTextView ()
+@interface ASTextKitComponentsTextView () {
+  // Prevent UITextView from updating contentOffset while deallocating: https://github.com/TextureGroup/Texture/issues/860
+  BOOL _deallocating;
+}
 @property (atomic, assign) CGRect threadSafeBounds;
 @end
 
@@ -31,10 +34,16 @@
   self = [super initWithFrame:frame textContainer:textContainer];
   if (self) {
     _threadSafeBounds = self.bounds;
+    _deallocating = NO;
   }
   return self;
 }
 
+- (void)dealloc
+{
+  _deallocating = YES;
+}
+
 - (void)setFrame:(CGRect)frame
 {
   ASDisplayNodeAssertMainThread();
@@ -49,6 +58,16 @@
   self.threadSafeBounds = bounds;
 }
 
+- (void)setContentOffset:(CGPoint)contentOffset
+{
+  if (_deallocating) {
+    return;
+  }
+  
+  [super setContentOffset:contentOffset];
+}
+
+
 @end
 
 @interface ASTextKitComponents ()