fix corner case in unused (#5066)

fixes #5065

lib/compress.js

@@ -7036,7 +7036,10 @@ merge(Compressor.prototype, {
                     if (compressor.option("default_values") && value && value.is_defined(compressor)) {
                         node = node.name;
                     } else {
+                        var save_drop = drop;
+                        drop = false;
                         var trimmed = trim_default(trimmer, node);
+                        drop = save_drop;
                         if (!trimmed && drop && value) value = value.drop_side_effect_free(compressor);
                         return trimmed;
                     }

test/compress/default-values.js

@@ -1874,3 +1874,19 @@ issue_5057_3: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5065: {
+    options = {
+        pure_getters: "strict",
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var [ a = console.log("PASS") ] = [ (A = 42).p ];
+    }
+    expect: {
+        var [ a = console.log("PASS") ] = [ (A = 42).p ];
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}