fix corner case in if_return (#5689)

fixes #5688

test/compress.js

@@ -126,6 +126,17 @@ function parse_test(file) {
                     croak(node);
                 }
                 var name = node.left.name;
+                assert.ok([
+                    "beautify",
+                    "expression",
+                    "mangle",
+                    "options",
+                    "rename",
+                ].indexOf(name) >= 0, tmpl("Unsupported setting {name} [{line},{col}]", {
+                    name: name,
+                    line: node.start.line,
+                    col: node.start.col,
+                }));
                 test[name] = evaluate(node.right);
                 return true;
             }

test/compress/if_return.js

@@ -2442,3 +2442,41 @@ issue_5649: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5688: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        L: do {
+            switch (console) {
+              default:
+                if (console)
+                    break;
+                if (FAIL_1)
+                    ;
+                else
+                    break L;
+                break;
+              case 42:
+                FAIL_2;
+            }
+        } while (console.log("PASS"));
+    }
+    expect: {
+        L: do {
+            switch (console) {
+              default:
+                if (console)
+                    break;
+                if (FAIL_1)
+                    break;
+                break L;
+              case 42:
+                FAIL_2;
+            }
+        } while (console.log("PASS"));
+    }
+    expect_stdout: "PASS"
+}