win32.c: suffix should be alnum

* win32/win32.c (fileattr_to_unixmode): built-in executable
  suffixes are alpha-numeric only, no needs to scan whole path,
  especially path separators.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53705 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

win32/win32.c

@@ -5337,6 +5337,7 @@ fileattr_to_unixmode(DWORD attr, const WCHAR *path)
 		}
 		break;
 	    }
+	    if (!iswalnum(*end)) break;
 	}
     }