"setIncompleteSubtype can be called only on a valid incomplete cache entry" crash from Pylance telemetry

Pyright crash from Pylance telemetry. It looks like this first appeared in 1.1.402. There have been about 2700 hits across 50 machines. I'm not sure why our dashboard code wasn't able to use the source maps to get function names for the call stack.

Filing in case the issue is apparent to you. We'll try to provide the function names in the future if needed.

```text
Error: Debug Failure. setIncompleteSubtype can be called only on a valid incomplete cache entry: prev cache entry?: false index=0 isPending=false evaluationCount=1
func (pyright.bundle.js:1:193372)
:1:201123
func ()
func (pyright.bundle.js:1:200418)
func (pyright.bundle.js:1:197181)
func (pyright.bundle.js:1:199857)
func (pyright.bundle.js:1:196992)
func (pyright.bundle.js:1:201990)
func (pyright.bundle.js:1:640967)
func (pyright.bundle.js:1:640298)
func (pyright.bundle.js:1:807786)
:1:891019
:1:890932
func (pyright.bundle.js:1:1216796)
func (pyright.bundle.js:1:846891)
func (pyright.bundle.js:1:728504)
func (pyright.bundle.js:1:724958)
func (pyright.bundle.js:1:730492)
func (pyright.bundle.js:1:708628)
:1:700245
func (pyright.bundle.js:1:834121)
:1:699913
func (pyright.bundle.js:1:986765)
func (pyright.bundle.js:1:648441)
func (pyright.bundle.js:1:649463)
func (pyright.bundle.js:1:699875)
:1:609003
:1:609608
```

Start with the reported assertion and the pyright.bundle.js stack from version 1.1.402, then investigate the corresponding cache-entry handling in the Pyright codebase. Reproduce the telemetry crash if possible and identify a focused regression test or other verification that confirms the assertion no longer occurs.

Written by the indexing model from the issue text.