Minor refactoring in try_index_step

Merges `if-let` and `if x.is_some() { ... }` blocks

Author: osa1

Diff for: compiler/rustc_typeck/src/check/place_op.rs

@@ -103,9 +103,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let method =
                 self.try_overloaded_place_op(expr.span, self_ty, &[input_ty], PlaceOp::Index);
 
-            let result = method.map(|ok| {
+            if let Some(result) = method {
                 debug!("try_index_step: success, using overloaded indexing");
-                let method = self.register_infer_ok_obligations(ok);
+                let method = self.register_infer_ok_obligations(result);
 
                 let mut adjustments = self.adjust_steps(autoderef);
                 if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
@@ -128,10 +128,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.apply_adjustments(base_expr, adjustments);
 
                 self.write_method_call(expr.hir_id, method);
-                (input_ty, self.make_overloaded_place_return_type(method).ty)
-            });
-            if result.is_some() {
-                return result;
+
+                return Some((input_ty, self.make_overloaded_place_return_type(method).ty));
             }
         }