Ensure consistent behavior for duplicate cookies

In the case of two (or more) cookies with the same name visible to the
current scope, so far we've been retrieving the first one we find for
`getCookie()`, but the last one for `getCookies()` (because in the
latter case we continued the loop and eventually overwrote a duplicate
cookie name in the returned result/object).

This change makes the behavior at least consistent, so there aren't
different cookies in the result for both calls.

Changing the api to include both cookies in the result seems reasonable.

For context: js-cookie#813

src/api.ts

@@ -64,7 +64,7 @@ function get<T extends string | undefined, U>(
   while ((match = scan.exec(document.cookie)) != null) {
     try {
       const found = decodeName(match[1])
-      jar[found] = decodeValue(match[2], found)
+      if (!(found in jar)) jar[found] = decodeValue(match[2], found)
       if (name === found) {
         break
       }

test/api.test.ts

@@ -214,6 +214,13 @@ describe('getCookie', () => {
     document.cookie = 'invalid=foo; expires=Thu, 01 Jan 1970 00:00:00 GMT'
   })
 
+  test('when there is a duplicate cookie', () => {
+    document.cookie = 'c=one; path=/'
+    document.cookie = 'c=two; path=/test'
+    expect(getCookie('c')).toBe('two') // 2nd (nested) cookie comes first...!
+    document.cookie = 'c=v; path=/test; expires=Thu, 01 Jan 1970 00:00:00 GMT'
+  })
+
   describe('decode', () => {
     test('with customized value decoding', () => {
       document.cookie = 'c=v'
@@ -271,6 +278,13 @@ describe('getCookies', () => {
     expect(getCookies()).toStrictEqual({})
   })
 
+  test('when there are duplicate cookies', () => {
+    document.cookie = 'c=one; path=/'
+    document.cookie = 'c=two; path=/test'
+    expect(getCookies()).toStrictEqual({ c: 'two' }) // 2nd (nested) cookie comes first...!
+    document.cookie = 'c=v; path=/test; expires=Thu, 01 Jan 1970 00:00:00 GMT'
+  })
+
   // github.com/js-cookie/js-cookie/issues/196
   test('when there is a cookie with malformed encoding in the name', () => {
     document.cookie = '%A1=foo'