add a debug_assert according to the comment

Guanqun Lu · Guanqun Lu · commit cf1e28eef969 · 2019-12-17T14:20:08.000+08:00
diff --git a/clippy_lints/src/methods/map_unwrap_or.rs b/clippy_lints/src/methods/map_unwrap_or.rs
@@ -61,6 +61,7 @@ pub(super) fn lint<'a, 'tcx>(
                 arg, suggest
             )
         } else {
+            debug_assert!(is_result);
             "called `map(f).unwrap_or(a)` on a Result value. \
              This can be done more directly by calling `map_or(a, f)` instead"
                 .to_string()

Original file line number	Diff line number	Diff line change
`@@ -61,6 +61,7 @@ pub(super) fn lint<'a, 'tcx>(`
`61`	`61`	`arg, suggest`
`62`	`62`	`)`
`63`	`63`	`} else {`
	`64`	`+ debug_assert!(is_result);`
`64`	`65`	"called `map(f).unwrap_or(a)` on a Result value. \
`65`	`66`	This can be done more directly by calling `map_or(a, f)` instead"
`66`	`67`	`.to_string()`