improve fix for #4325 (#4649)

lib/compress.js

@@ -7003,6 +7003,8 @@ merge(Compressor.prototype, {
                 // always shallow clone to ensure stripping of negated IIFEs
                 self = self.clone();
                 self.expression = exp.clone();
+                // avoid extraneous traversal
+                if (exp._squeezed) self.expression._squeezed = true;
             }
             if (self instanceof AST_New) {
                 var fn = exp;