Fix coercing arity in baseCurry.

lodash.js

@@ -1624,7 +1624,7 @@
      */
     function baseCurry(func, bitmask, arity) {
       if (typeof arity != 'number') {
-        arity = +arity || (func ? func.length : 0);
+        arity = arity == null ? (func ? func.length : 0) : (+arity || 0);
       }
       return createWrapper([func, bitmask, arity]);
     }

test/test.js

@@ -2229,7 +2229,7 @@
       deepEqual(curried(1, 2, 3, 4), expected);
     });
 
-    test('should allow specifying `arity`', 3, function(){
+    test('should allow specifying `arity`', 3, function() {
       var curried = _.curry(fn, 3),
           expected = [1, 2, 3];
 
@@ -2238,6 +2238,21 @@
       deepEqual(curried(1, 2, 3), expected);
     });
 
+    test('should coerce `arity` to a number', 2, function() {
+      var values = ['0', 'xyz'],
+          expected = _.map(values, _.constant([]));
+
+      var actual = _.map(values, function(arity) {
+        var curried = _.curry(fn, arity);
+        return curried();
+      });
+
+      deepEqual(actual, expected);
+
+      curried = _.curry(fn, '2');
+      deepEqual(curried(1)(2), [1, 2]);
+    });
+
     test('should work with partialed methods', 2, function() {
       var curried = _.curry(fn),
           expected = [1, 2, 3, 4];