Properly load top-level constant initializers from multifile classes

Before Kotlin 1.3-M2 we didn't write `has_field` flag for constants
 inside multifile classes. Now we write and rely on this when
 trying to load constant initializers, which is totally fine for
 binaries that were compiled with the 1.3-M2 or newer version.
 Unfortunately, constant initializers will not be loaded for old binaries.

 One way is to avoid relying on this flag, but then we'll get other
 problems (e.g. 3345dc81fd).

 Therefore, for binaries that were compiled with at least 1.3-M2 version,
 we'll rely on the flag, otherwise, we won't.

core/metadata.jvm/src/org/jetbrains/kotlin/metadata/jvm/deserialization/JvmProtoBufUtil.kt

@@ -104,14 +104,16 @@ object JvmProtoBufUtil {
     fun getJvmFieldSignature(
         proto: ProtoBuf.Property,
         nameResolver: NameResolver,
-        typeTable: TypeTable
+        typeTable: TypeTable,
+        requireHasFieldFlag: Boolean = true
     ): JvmMemberSignature.Field? {
         val signature = proto.getExtensionOrNull(JvmProtoBuf.propertySignature) ?: return null
-        val field = if (signature.hasField()) signature.field else return null
+        val field = if (signature.hasField()) signature.field else null
+        if (field == null && requireHasFieldFlag) return null
 
-        val name = if (field.hasName()) field.name else proto.name
+        val name = if (field != null && field.hasName()) field.name else proto.name
         val desc =
-            if (field.hasDesc()) nameResolver.getString(field.desc)
+            if (field != null && field.hasDesc()) nameResolver.getString(field.desc)
             else mapTypeDefault(proto.returnType(typeTable), nameResolver) ?: return null
 
         return JvmMemberSignature.Field(nameResolver.getString(name), desc)