Don't Accept Websocket Upgrade on non-Websocket Routes

[fhessel]

Describe the bug
The server accept websocket upgrades on non-websocket routes.

How To Reproduce
Steps to reproduce the behavior (example):

1. Flash the chat example to the device.
2. Open the chat page in a browser tab.
3. Keep the tab open and flash another example without websockets to the device.
4. Click on the "Connect" button to send a websocket request.

Expected Behavior
The server should reject the websocket upgrade request.

Actual Behavior
The server goes into upgrade mode:

[HTTPS:I] New connection. Socket FID=55
[HTTPS:I] Request: GET /chat (FID=55)
[HTTPS:I] Upgrading to WS, FID=55

This is followed by a Guru Meditation / Panic:

Guru Meditation Error: Core  1 panic'ed (InstrFetchProhibited). Exception was unhandled.

ESP32 Module
ESP32 WROVER 16/16

Software (please complete the following information if applicable)

• IDE and Version: PlatformIO - Home 2.3.3, Core 4.0.3
• OS: Debian Buster
• Client used to access the server: Firefox 60.9.0esr (64-bit)

Additional context
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