Back out "Remove awkward assert"

This backs out commit 6126237bc4.

src/reader.rs

@@ -4848,7 +4848,13 @@ impl<'a> Reader<'a> {
         }
 
         let el = &self.data.command_line;
+        let autosuggestion = &self.autosuggestion;
         if self.is_at_line_with_autosuggestion() {
+            assert!(string_prefixes_string_maybe_case_insensitive(
+                autosuggestion.icase,
+                &el.text()[autosuggestion.search_string_range.clone()],
+                &autosuggestion.text
+            ));
             return;
         }