urlapi: fix heap buffer overflow

`u->path = Curl_memdup(path, pathlen + 1);` accesses bytes after the null-terminator.

```
==2676==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x04d48c75 at pc 0x0112708a bp 0x006fb7e0 sp 0x006fb3c4
READ of size 78 at 0x04d48c75 thread T0
    #0 0x1127089 in __asan_wrap_memcpy D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_common_interceptors.inc:840
    #1 0x1891a0e in Curl_memdup C:\actions-runner\_work\client\client\third_party\curl\lib\strdup.c:97
    #2 0x18db4b0 in parseurl C:\actions-runner\_work\client\client\third_party\curl\lib\urlapi.c:1297
    #3 0x18db819 in parseurl_and_replace C:\actions-runner\_work\client\client\third_party\curl\lib\urlapi.c:1342
    #4 0x18d6e39 in curl_url_set C:\actions-runner\_work\client\client\third_party\curl\lib\urlapi.c:1790
    #5 0x1877d3e in parseurlandfillconn C:\actions-runner\_work\client\client\third_party\curl\lib\url.c:1768
    #6 0x1871acf in create_conn C:\actions-runner\_work\client\client\third_party\curl\lib\url.c:3403
    #7 0x186d8dc in Curl_connect C:\actions-runner\_work\client\client\third_party\curl\lib\url.c:3888
    #8 0x1856b78 in multi_runsingle C:\actions-runner\_work\client\client\third_party\curl\lib\multi.c:1982
    #9 0x18531e3 in curl_multi_perform C:\actions-runner\_work\client\client\third_party\curl\lib\multi.c:2756
```

Closes #11560

lib/urlapi.c

@@ -1109,6 +1109,7 @@ static CURLUcode parseurl(const char *url, CURLU *u, unsigned int flags)
     if('/' == path[0] && STARTS_WITH_URL_DRIVE_PREFIX(&path[1])) {
       /* This cannot be done with strcpy, as the memory chunks overlap! */
       path++;
+      pathlen--;
     }
 #endif