has_side_effects() should take AST_Switch.expression into account

fixes #1698

lib/compress.js

@@ -1610,9 +1610,13 @@ merge(Compressor.prototype, {
         def(AST_Block, function(compressor){
             return any(this.body, compressor);
         });
+        def(AST_Switch, function(compressor){
+            return this.expression.has_side_effects(compressor)
+                || any(this.body, compressor);
+        });
         def(AST_Case, function(compressor){
-            return any(this.body, compressor)
-                || this.expression.has_side_effects(compressor);
+            return this.expression.has_side_effects(compressor)
+                || any(this.body, compressor);
         });
         def(AST_Try, function(compressor){
             return any(this.body, compressor)

test/compress/switch.js

@@ -593,3 +593,24 @@ if_switch_typeof: {
         a;
     }
 }
+
+issue_1698: {
+    options = {
+        side_effects: true,
+    }
+    input: {
+        var a = 1;
+        !function() {
+            switch (a++) {}
+        }();
+        console.log(a);
+    }
+    expect: {
+        var a = 1;
+        !function() {
+            switch (a++) {}
+        }();
+        console.log(a);
+    }
+    expect_stdout: "2"
+}