[MDCProgressView] Execute completion block when setHidden:animated:co…

…mpletion is called sequentially (#787)

* [MDCInkView] cancelAllAnimationsAnimated should support disabling animation

* Call completion block immediately rather than storing as a property.

* Add nil check for completion block

components/ProgressView/src/MDCProgressView.m

@@ -156,8 +156,12 @@ - (void)setHidden:(BOOL)hidden {
 - (void)setHidden:(BOOL)hidden
          animated:(BOOL)animated
        completion:(void (^__nullable)(BOOL finished))completion {
-  if (hidden == self.hidden)
+  if (hidden == self.hidden) {
+    if (completion) {
+      completion(YES);
+    }
     return;
+  }
 
   void (^animations)(void);