udev: ensure there is space for trailing NUL before calling sprintf

sprintf will write 5 characters, as it adds a trailing NUL byte.

Reported on yeswehack.com as:
YWH-PGM9780-62

Follow-up for 8cfcf9980a

src/basic/device-nodes.c

@@ -6,6 +6,7 @@
 
 #include "device-nodes.h"
 #include "path-util.h"
+#include "stdio-util.h"
 #include "string-util.h"
 #include "utf8.h"
 
@@ -38,10 +39,10 @@ int encode_devnode_name(const char *str, char *str_enc, size_t len) {
 
                 } else if (str[i] == '\\' || !allow_listed_char_for_devnode(str[i], NULL)) {
 
-                        if (len-j < 4)
+                        if (len-j < 5)
                                 return -EINVAL;
 
-                        sprintf(&str_enc[j], "\\x%02x", (unsigned char) str[i]);
+                        assert_se(snprintf_ok(&str_enc[j], 5, "\\x%02x", (unsigned char) str[i]));
                         j += 4;
 
                 } else {