Auto merge of rust-lang#13940 - nlydv:unwrap-panic, r=lnicola

Fix panicking Option unwraping in match arm analysis

Hi, first PR here!

I've noticed my IDE sometimes briefly becoming pretty slow to respond while writing Rust. When checking the logs I found reams of this same error repeating itself.

```
thread 'Worker' panicked at 'called `Option::unwrap()` on a `None` value'
crates/ide-assists/src/handlers/convert_match_to_let_else.rs:90:46
```

RA seemed to have been panicking on virtually every keystroke I made whenever I was part way through writing/refactoring a match statement of relevance to this assist.

The fix in this PR should be self-explanatory.

Author: bors

crates/ide-assists/src/handlers/convert_match_to_let_else.rs

@@ -87,7 +87,7 @@ fn find_arms(
     let mut extracting = None;
     let mut diverging = None;
     for arm in arms {
-        if ctx.sema.type_of_expr(&arm.expr().unwrap()).unwrap().original().is_never() {
+        if ctx.sema.type_of_expr(&arm.expr()?)?.original().is_never() {
             diverging = Some(arm);
         } else {
             extracting = Some(arm);