Merge pull request libgit2#4805 from libgit2/signed_char

path validation: `char` is not signed by default.

Author: ethomson

src/path.c

@@ -1662,7 +1662,7 @@ GIT_INLINE(bool) verify_dotgit_ntfs_generic(const char *name, size_t len, const
 			saw_tilde = 1;
 		} else if (i >= 6) {
 			return true;
-		} else if (name[i] < 0) {
+		} else if ((unsigned char)name[i] > 127) {
 			return true;
 		} else if (git__tolower(name[i]) != shortname_pfix[i]) {
 			return true;