Fixed incorrect output size clamping

[mbezuidenhout]

Description:

Fixed incorrect output size clamping. Code was reading past the end of const char* hex

out_len is the maximum size of the output and thus the value of bytes_out cannot be larger than out_len.

Checklist:

• [x] The pull request is done against the latest development branch
• [x] Only relevant files were touched
• [x] Only one feature/fix was added per PR and the code change compiles without warnings
• [x] The code change is tested and works with Tasmota core ESP8266 V.2.7.6
• [x] The code change is tested and works with Tasmota core ESP32 V.3.0.0
• [x] I accept the CLA.

[s-hadinger]

@arendst This looks ok to me.