Zigbee fix for visual map

[s-hadinger]

Description:

Fixes for Zigbee visual map:

• show a message if it was not possible to load vis.js library
• avoid an infinite loop with ZbMap when a device falsely reports more devices that it actually knows

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works on Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works on Tasmota core ESP32 V.1.0.4.2
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass