Fill the ring-buffer with the fallback value

Fill with the pointer to the root position, instead of zero and
comparing later.  Also suppress a false warning by Visual C++.

```
file.c(4759): warning C4090: 'function': different 'const' qualifiers
```

1 files changed, 1 insertions, 2 deletions

diff --git a/file.c b/file.c
index e8e4b1d541..6e6dfbca17 100644
--- a/file.c
+++ b/file.c
@@ -4756,7 +4756,7 @@ rb_file_dirname_n(VALUE fname, int n)
 	    break;
 	  default:
 	    seps = ALLOCV_N(const char *, sepsv, n);
-	    MEMZERO(seps, const char *, n);
+	    for (i = 0; i < n; ++i) seps[i] = root;
 	    i = 0;
 	    for (p = root; p < end; ) {
 		if (isdirsep(*p)) {
@@ -4772,7 +4772,6 @@ rb_file_dirname_n(VALUE fname, int n)
 	    }
 	    p = seps[i];
 	    ALLOCV_END(sepsv);
-	    if (!p) p = root;
 	    break;
 	}
     }