use a let-chain in needless_bool (#15444)

This is a small thing I noticed while looking into
#8014. Since I ultimately
decided not to change the code as a response to the issue, I'm now left
with this one commit, and I feel a bit unsure about making a PR just for
that. This is a problem I have relatively often, so I'd like to know
whether I should to batch these small changes somehow, or whether these
small PRs are fine after all

changelog: none

Author: samueltardieu

clippy_lints/src/needless_bool.rs

@@ -166,7 +166,9 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
                     applicability,
                 );
             };
-            if let Some((a, b)) = fetch_bool_block(then).and_then(|a| Some((a, fetch_bool_block(else_expr)?))) {
+            if let Some(a) = fetch_bool_block(then)
+                && let Some(b) = fetch_bool_block(else_expr)
+            {
                 match (a, b) {
                     (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
                         span_lint(