Effects: Account for pre-jQuery-3.2.0 bugs

Followup to #264

See
jquery/jquery@6d43dc4

Author: dmethvin

test/effects.js

@@ -5,16 +5,20 @@ QUnit.test( "jQuery.easing", function( assert ) {
 		easingCallCount = 0,
 		animComplete = assert.async();
 
-	assert.expect( 4 );
+	assert.expect( 5 );
 
 	jQuery.easing.testOld = function( p, n, firstNum, diff ) {
 		assert.ok( false, "should not have been called" );
 	};
 
 	jQuery.easing.testNew = function( p ) {
-		if ( ++easingCallCount < 3 ) {
-			assert.ok( p > lastP, "called, percentage is increasing" );
-			lastP = p;
+		if ( ++easingCallCount < 4 ) {
+			if ( p === 0 && p === lastP ) {
+				assert.ok( true, "p===0 called twice before jQuery 3.2.0" );
+			} else {
+				assert.ok( p > lastP, "called, percentage is increasing" );
+				lastP = p;
+			}
 		}
 
 		// Linear