Effects: First step() call should match :animated selector

(cherry picked from commit 08581447)

Fixes #14623
Closes gh-1473

src/effects.js

@@ -616,8 +616,11 @@ jQuery.fx.tick = function() {
 };
 
 jQuery.fx.timer = function( timer ) {
-	if ( timer() && jQuery.timers.push( timer ) ) {
+	jQuery.timers.push( timer );
+	if ( timer() ) {
 		jQuery.fx.start();
+	} else {
+		jQuery.timers.pop();
 	}
 };
 

test/unit/effects.js

@@ -1608,6 +1608,21 @@ test("Animation callback should not show animated element as :animated (#7157)",
 	this.clock.tick( 100 );
 });
 
+test("Initial step callback should show element as :animated (#14623)", 1, function() {
+	var foo = jQuery( "#foo" );
+
+	foo.animate({
+		opacity: 0
+	}, {
+		duration: 100,
+		step: function() {
+			ok( foo.is(":animated"), "The element matches :animated inside step function" );
+		}
+	});
+	this.clock.tick( 1 );
+	foo.stop();
+});
+
 test( "hide called on element within hidden parent should set display to none (#10045)", 3, function() {
 	var hidden = jQuery(".hidden"),
 		elems = jQuery("<div>hide</div><div>hide0</div><div>hide1</div>");