Fix translation of copy() fun in data class

Fix translation of copy() function in data class which has secondary
constructor in JS BE. See KT-16717.

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -6520,6 +6520,12 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/dataClasses/copy/withGenericParameter.kt");
                 doTest(fileName);
             }
+
+            @TestMetadata("withSecondaryConstructor.kt")
+            public void testWithSecondaryConstructor() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/dataClasses/copy/withSecondaryConstructor.kt");
+                doTest(fileName);
+            }
         }
 
         @TestMetadata("compiler/testData/codegen/box/dataClasses/equals")

js/js.translator/src/org/jetbrains/kotlin/js/translate/declaration/JsDataClassGenerator.java

@@ -91,7 +91,8 @@ class JsDataClassGenerator extends DataClassMethodGenerator {
         }
 
         ClassDescriptor classDescriptor = (ClassDescriptor) function.getContainingDeclaration();
-        ClassConstructorDescriptor constructor = classDescriptor.getConstructors().iterator().next();
+        ClassConstructorDescriptor constructor = classDescriptor.getUnsubstitutedPrimaryConstructor();
+        assert constructor != null : "Data class should have primary constructor: " + classDescriptor;
 
         JsExpression constructorRef = context.getInnerReference(constructor);