fix corner case in collapse_vars (#5505)

fixes #5504

lib/compress.js

@@ -2356,7 +2356,7 @@ Compressor.prototype.compress = function(node) {
                         if (prop.key instanceof AST_Node) prop.key = prop.key.transform(tt);
                         if (prop.static) {
                             if (prop instanceof AST_ClassField) {
-                                props.push(prop);
+                                if (prop.value) props.push(prop);
                             } else if (prop instanceof AST_ClassInit) {
                                 props.unshift(prop);
                             }

test/compress/classes.js

@@ -3179,3 +3179,25 @@ issue_5502: {
     expect_stdout: "PASS 42"
     node_version: ">=12"
 }
+
+issue_5504: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        "use strict";
+        var a;
+        console.log((a = 42, class {
+            static p;
+        }).p);
+    }
+    expect: {
+        "use strict";
+        var a;
+        console.log((a = 42, class {
+            static p;
+        }).p);
+    }
+    expect_stdout: "undefined"
+    node_version: ">=12"
+}