path: move branch to the correct location

This code branch only makes sense when i === length. Otherwise it'll
already be handled.

PR-URL: nodejs#28556
Fixes: nodejs#28549
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

lib/path.js

@@ -518,11 +518,11 @@ const win32 = {
           lastCommonSep = 3;
         }
       }
+      if (lastCommonSep === -1)
+        lastCommonSep = 0;
     }
 
     let out = '';
-    if (lastCommonSep === -1)
-      lastCommonSep = 0;
     // Generate the relative path based on the path difference between `to` and
     // `from`
     for (i = fromStart + lastCommonSep + 1; i <= fromEnd; ++i) {