Fix #11415: Stop non-negative prop undershoot on animation.

This doesn't fix *all* of them (see the ticket for a supposedly complete list) but these were already handy so it was relatively cheap to fix them. If you need others fixed, add a custom step function as was done here. Thanks @scott_gonzalez!

src/effects.js

@@ -634,9 +634,8 @@ jQuery.extend( jQuery.fx, {
 	}
 });
 
-// Adds width/height step functions
-// Do not set anything below 0
-jQuery.each([ "width", "height" ], function( i, prop ) {
+// Ensure props that can't be negative don't go there on undershoot easing
+jQuery.each( fxAttrs.concat.apply( [], fxAttrs ), function( i, prop ) {
 	jQuery.fx.step[ prop ] = function( fx ) {
 		jQuery.style( fx.elem, prop, Math.max(0, fx.now) + fx.unit );
 	};

test/unit/effects.js

@@ -263,6 +263,15 @@ test("animate negative height", function() {
 	});
 });
 
+test("animate negative padding", function() {
+	expect(1);
+	stop();
+	jQuery("#foo").animate({ paddingBottom: -100 }, 100, function() {
+		equal( jQuery(this).css("paddingBottom"), "0px", "Verify paddingBottom." );
+		start();
+	});
+});
+
 test("animate block as inline width/height", function() {
 	expect(3);