fix corner case in collapse_vars (#5482)

fixes #5481

test/compress/classes.js

@@ -2852,3 +2852,33 @@ issue_5436: {
     expect_stdout: "PASS"
     node_version: ">=12"
 }
+
+issue_5481: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        "use strict";
+        var a = "FAIL 1", log = console.log;
+        try {
+            a = "PASS";
+            (class extends 42 {});
+            log("FAIL 2", a);
+        } catch (e) {
+            log(a);
+        }
+    }
+    expect: {
+        "use strict";
+        var a = "FAIL 1", log = console.log;
+        try {
+            a = "PASS";
+            (class extends 42 {});
+            log("FAIL 2", a);
+        } catch (e) {
+            log(a);
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}

test/ufuzz/index.js

@@ -2398,7 +2398,7 @@ function patch_try_catch(orig, toplevel) {
                     "throw " + match[1] + ";",
                 ].join("\n");
             }
-            var new_code = code.slice(0, index) + insert + code.slice(index) + tail_throw;
+            var new_code = code.slice(0, index) + insert + code.slice(index) + tail_throw + "var UFUZZ_ERROR;";
             var result = run_code(new_code, toplevel);
             if (!sandbox.is_error(result)) {
                 if (!stack.filled && match[1]) stack.push({