enhance conditionals (#2758)

`x ? y || z : z` --> `x && y || z`

lib/compress.js

@@ -5278,6 +5278,20 @@ merge(Compressor.prototype, {
                 consequent
             ]).optimize(compressor);
         }
+        // x ? y || z : z --> x && y || z
+        if (consequent instanceof AST_Binary
+            && consequent.operator == "||"
+            && consequent.right.equivalent_to(alternative)) {
+            return make_node(AST_Binary, self, {
+                operator: "||",
+                left: make_node(AST_Binary, self, {
+                    operator: "&&",
+                    left: self.condition,
+                    right: consequent.left
+                }),
+                right: alternative
+            }).optimize(compressor);
+        }
         var in_bool = compressor.in_boolean_context();
         if (is_true(self.consequent)) {
             if (is_false(self.alternative)) {