Fix AssertionError on property generation in multi-file classes

See 4a533168d9 for the original change which
introduced the problem

Note that the added test case _was not failing_ before the change. It's added
because there were no tests on multi-file class behavior in light classes mode
at all. The actual repro for the problem is difficult to make a test from

 #KT-12755 Fixed

compiler/tests/org/jetbrains/kotlin/asJava/CompilerLightClassTestGenerated.java

@@ -88,6 +88,12 @@ public class CompilerLightClassTestGenerated extends AbstractCompilerLightClassT
             doTest(fileName);
         }
 
+        @TestMetadata("MultiFile.kt")
+        public void testMultiFile() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/asJava/lightClasses/facades/MultiFile.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("SingleFile.kt")
         public void testSingleFile() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/asJava/lightClasses/facades/SingleFile.kt");