Fix #14313: Optimize jQuery.merge for size. Close gh-1344.

src/core.js

@@ -552,18 +552,14 @@ jQuery.extend({
 	},
 
 	merge: function( first, second ) {
-		var l = second.length,
+		var l = +second.length,
 			i = first.length,
 			j = 0;
 
-		if ( typeof l === "number" ) {
+		if ( l ) {
 			for ( ; j < l; j++ ) {
 				first[ i++ ] = second[ j ];
 			}
-		} else {
-			while ( second[j] !== undefined ) {
-				first[ i++ ] = second[ j++ ];
-			}
 		}
 
 		first.length = i;