Disabling one completion and linting provider prevents showing completions

[dalthviz]

Problem Description

Disabling a completion provider prevents showing completions even if there are still more providers enabled

What steps reproduce the problem?

1. Go to Preferences > Completion and Linting and uncheck Enable Fallback Provider
2. Try to get completions from the Editor (it doesn't work)
3. Check again the Enable Fallback Provider from the preferences
4. Completions from the Editor start working again

Preview

What is the expected output? What do you see instead?

To be able to disable an individual provider without affecting getting completions from other providers

Versions

• Spyder version: 5.4.5 (standalone)
• Python version: 3.8.10 64-bit
• Qt version: 5.15.2
• PyQt5 version: 5.15.9
• Operating System: Windows-10-10.0.19045-SP0

[ccordoba12]

I think this is serious enough to warrant delaying 5.5.0 for a few days so we try to fix it.