prevent negative array-offset getting

The modulo operation can result in a negative number,
while the list of window handles is always a 0-based array

Author: webmaster777

src/Codeception/Module/WebDriver.php

@@ -3503,8 +3503,12 @@ protected function getRelativeTabHandle($offset)
         }
         $handle = $this->webDriver->getWindowHandle();
         $handles = $this->webDriver->getWindowHandles();
-        $idx = array_search($handle, $handles);
-        return $handles[($idx + $offset) % count($handles)];
+        $currentHandleIdx = array_search($handle, $handles);
+        $newHandleIdx = ($currentHandleIdx + $offset) % count($handles);
+        if ($newHandleIdx < 0) {
+            $newHandleIdx = count($handles) + $newHandleIdx;
+        }
+        return $handles[$newHandleIdx];
     }
 
     /**