fix corner case in hoist_vars (#4860)

fixes #4859

lib/compress.js

@@ -6942,9 +6942,7 @@ merge(Compressor.prototype, {
             if (defs.length > 0) {
                 // try to merge in assignments
                 insert_vars(self.body);
-                defs = make_node(AST_Var, self, {
-                    definitions: defs
-                });
+                defs = make_node(AST_Var, self, { definitions: defs });
                 hoisted.push(defs);
             }
         }
@@ -8367,12 +8365,14 @@ merge(Compressor.prototype, {
     AST_Definitions.DEFMETHOD("to_assignments", function() {
         var assignments = this.definitions.reduce(function(a, defn) {
             var def = defn.name.definition();
-            if (defn.value) {
+            var value = defn.value;
+            if (value) {
+                if (value instanceof AST_Sequence) value = value.clone();
                 var name = make_node(AST_SymbolRef, defn.name, defn.name);
                 a.push(make_node(AST_Assign, defn, {
-                    operator : "=",
-                    left     : name,
-                    right    : defn.value
+                    operator: "=",
+                    left: name,
+                    right: value,
                 }));
                 def.references.push(name);
             }