patch 9.0.2033: gcc overflow-warning for f_resolve

patch 9.0.2033: gcc overflow-warning for f_resolve

Problem:  gcc overflow-warning for f_resolve
Solution: use pointer p instead of pointer q[-1]

Suppress the following warning:
```
filepath.c: In function ‘f_resolve’:
filepath.c:2162:27: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 2162 |                     q[-1] = NUL;
```

Closes: #13352
closes: #13353

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ken Takata <kentkt@csc.jp>