Fixed bug that Str::replaceLast with empty search cannot work as expected. (#6217)

Author: luck-xj

src/Str.php

@@ -601,6 +601,10 @@ public static function replaceFirst(string $search, string $replace, string $sub
      */
     public static function replaceLast(string $search, string $replace, string $subject): string
     {
+        if ($search == '') {
+            return $subject;
+        }
+
         $position = strrpos($subject, $search);
 
         if ($position !== false) {

tests/StrTest.php

@@ -558,4 +558,10 @@ public function testConvertCase()
             $this->assertSame($item[0], Str::convertCase(...$item[1]));
         }
     }
+
+    public function testReplaceLast()
+    {
+        $this->assertSame('Hello earth', Str::replaceLast('world', 'earth', 'Hello world'));
+        $this->assertSame('Hello world', Str::replaceLast('', 'earth', 'Hello world'));
+    }
 }