Fix safe call on a static method in JVM back-end

#KT-5796 Fixed

compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -1754,8 +1754,10 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
                 return StackValue.field(type, type, descriptor.getName().asString(), true);
             }
             ClassDescriptor classObjectDescriptor = classDescriptor.getClassObjectDescriptor();
-            assert classObjectDescriptor != null : "Class object is not found for " + descriptor;
-            return StackValue.singleton(classObjectDescriptor, typeMapper);
+            if (classObjectDescriptor != null) {
+                return StackValue.singleton(classObjectDescriptor, typeMapper);
+            }
+            return StackValue.none();
         }
 
         if (descriptor instanceof TypeParameterDescriptor) {

compiler/testData/codegen/box/safeCall/staticCall.kt

@@ -0,0 +1 @@
+fun box(): String = if (Thread?.currentThread() != null) "OK" else "Fail"

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java

@@ -5647,6 +5647,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
         
+        @TestMetadata("staticCall.kt")
+        public void testStaticCall() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/safeCall/staticCall.kt");
+            doTest(fileName);
+        }
+        
     }
     
     @TestMetadata("compiler/testData/codegen/box/samConstructors")