JS: fix crash when js function contains assignment with bad LHS

Fix KT-20905

compiler/testData/diagnostics/testsWithJsStdLib/jsCode/badAssignment.kt

@@ -0,0 +1,4 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+fun Int.foo(x: Int) {
+    js("this = x<!JSCODE_ERROR!><!>;")
+}

compiler/testData/diagnostics/testsWithJsStdLib/jsCode/badAssignment.txt

@@ -0,0 +1,3 @@
+package
+
+public fun kotlin.Int.foo(/*0*/ x: kotlin.Int): kotlin.Unit

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithJsStdLibGenerated.java

@@ -374,6 +374,12 @@ public class DiagnosticsTestWithJsStdLibGenerated extends AbstractDiagnosticsTes
             doTest(fileName);
         }
 
+        @TestMetadata("badAssignment.kt")
+        public void testBadAssignment() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithJsStdLib/jsCode/badAssignment.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("deleteOperation.kt")
         public void testDeleteOperation() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithJsStdLib/jsCode/deleteOperation.kt");

js/js.parser/src/com/google/gwt/dev/js/rhino/IRFactory.java

@@ -341,18 +341,12 @@ public class IRFactory {
             default:
                 // TODO: This should be a ReferenceError--but that's a runtime 
                 //  exception. Should we compile an exception into the code?
-                reportError("msg.bad.lhs.assign");
+                ts.reportSyntaxError("msg.bad.lhs.assign", null);
         }
         
         return new Node(TokenStream.ASSIGN, left, right, nodeOp, location);
     }
 
-    private void reportError(String msgResource) {
-
-        String message = Context.getMessage0(msgResource);
-        ts.reportSyntaxError(message, null);
-    }
-
     // Only needed to get file/line information. Could create an interface
     // that TokenStream implements if we want to make the connection less
     // direct.