fix dead_code on AST_Destructuring (#2392)

fixes #2383

lib/compress.js

@@ -3315,7 +3315,21 @@ merge(Compressor.prototype, {
     });
 
     AST_Definitions.DEFMETHOD("remove_initializers", function(){
-        this.definitions.forEach(function(def){ def.value = null });
+        var decls = [];
+        this.definitions.forEach(function(def) {
+            if (def.name instanceof AST_SymbolDeclaration) {
+                def.value = null;
+                decls.push(def);
+            } else def.name.walk(new TreeWalker(function(node) {
+                if (node instanceof AST_SymbolDeclaration) {
+                    decls.push(make_node(AST_VarDef, def, {
+                        name: node,
+                        value: null
+                    }));
+                }
+            }));
+        });
+        this.definitions = decls;
     });
 
     AST_Definitions.DEFMETHOD("to_assignments", function(compressor){

test/compress/dead-code.js

@@ -560,3 +560,64 @@ global_fns: {
         "RangeError",
     ]
 }
+
+issue_2383_1: {
+    options = {
+        conditionals: true,
+        dead_code: true,
+        evaluate: true,
+    }
+    input: {
+        if (0) {
+            var {x, y} = foo();
+        }
+    }
+    expect: {
+        var x, y;
+    }
+}
+
+issue_2383_2: {
+    options = {
+        conditionals: true,
+        dead_code: true,
+        evaluate: true,
+    }
+    input: {
+        if (0) {
+            var {
+                x = 0,
+                y: [ w, , { z, p: q = 7 } ] = [ 1, 2, { z: 3 } ]
+            } = {};
+        }
+        console.log(x, q, w, z);
+    }
+    expect: {
+        var x, w, z, q;
+        console.log(x, q, w, z);
+    }
+    expect_stdout: "undefined undefined undefined undefined"
+    node_version: ">=6"
+}
+
+issue_2383_3: {
+    options = {
+        conditionals: true,
+        dead_code: true,
+        evaluate: true,
+    }
+    input: {
+        var b = 7, y = 8;
+        if (0) {
+            var a = 1, [ x, y, z ] = [ 2, 3, 4 ], b = 5;
+        }
+        console.log(a, x, y, z, b);
+    }
+    expect: {
+        var b = 7, y = 8;
+        var a, x, y, z, b;
+        console.log(a, x, y, z, b);
+    }
+    expect_stdout: "undefined undefined 8 undefined 7"
+    node_version: ">=6"
+}