lua: LuaPushStringBuffer optimization

Only use a temp buffer when really necessary, which is when the
buffer size is not a multiple of 4.

src/util-lua.c

@@ -236,18 +236,22 @@ void LuaPrintStack(lua_State *state) {
 
 int LuaPushStringBuffer(lua_State *luastate, const uint8_t *input, size_t input_len)
 {
-    /* we're using a buffer sized at a multiple of 4 as lua_pushlstring generates
-     * invalid read errors in valgrind otherwise. Adding in a nul to be sure.
-     *
-     * Buffer size = len + 1 (for nul) + whatever makes it a multiple of 4 */
-    size_t buflen = input_len + 1 + ((input_len + 1) % 4);
-    uint8_t buf[buflen];
-    memset(buf, 0x00, buflen);
-    memcpy(buf, input, input_len);
-    buf[input_len] = '\0';
-
-    /* return value through luastate, as a luastring */
-    lua_pushlstring(luastate, (char *)buf, input_len);
+    if (input_len % 4 != 0) {
+        /* we're using a buffer sized at a multiple of 4 as lua_pushlstring generates
+         * invalid read errors in valgrind otherwise. Adding in a nul to be sure.
+         *
+         * Buffer size = len + 1 (for nul) + whatever makes it a multiple of 4 */
+        size_t buflen = input_len + 1 + ((input_len + 1) % 4);
+        uint8_t buf[buflen];
+        memset(buf, 0x00, buflen);
+        memcpy(buf, input, input_len);
+        buf[input_len] = '\0';
+
+        /* return value through luastate, as a luastring */
+        lua_pushlstring(luastate, (char *)buf, input_len);
+    } else {
+        lua_pushlstring(luastate, (char *)input, input_len);
+    }
     return 1;
 }