fix issue jquery-validation#2047:Empty maxlength fails validation

src/core.js

@@ -1461,7 +1461,9 @@ $.extend( $.validator, {
 		// https://jqueryvalidation.org/maxlength-method/
 		maxlength: function( value, element, param ) {
 			var length = Array.isArray( value ) ? value.length : this.getLength( value, element );
-			return this.optional( element ) || length <= param;
+
+			// If param is equal to 0, it means maxlength has no limitation
+			return this.optional( element ) || param === 0 || length <= param;
 		},
 
 		// https://jqueryvalidation.org/rangelength-method/

test/index.html

@@ -211,6 +211,7 @@ <h3></h3>
 		</ul>
 	</form>
 	<form id="form" action="formaction">
+		<input type="text" name="action" value="" id="emptyText">
 		<input type="text" name="action" value="Test" id="text1">
 		<input type="text" name="text2" value="" id="text1b">
 		<input type="text" name="text2" value="T " id="text1c">

test/methods.js

@@ -327,8 +327,12 @@ QUnit.test( "maxlength", function( assert ) {
 	var v = jQuery( "#form" ).validate(),
 		method = $.validator.methods.maxlength,
 		param = 4,
-		e = $( "#text1, #text2, #text3" );
+		e = $( "#emptyText" );
+
+	assert.ok( method.call( v, e[ 0 ].value, e[ 0 ], 0 ), "Valid text input" );
 
+	e = $( "#text1, #text2, #text3" );
+	assert.ok( method.call( v, e[ 0 ].value, e[ 0 ], 0 ), "Valid text input" );
 	assert.ok( method.call( v, e[ 0 ].value, e[ 0 ], param ), "Valid text input" );
 	assert.ok( method.call( v, e[ 1 ].value, e[ 1 ], param ), "Valid text input" );
 	assert.ok( !method.call( v, e[ 2 ].value, e[ 2 ], param ), "Invalid text input" );