Show expect / actual gutter even for incomplete compatibility

So #KT-18445 Fixed
So #KT-21115 Fixed

idea/testData/multiModuleLineMarker/fromCommonToJvmImpl/common/common.kt

@@ -4,6 +4,10 @@ expect class Header {
     fun foo(): Int
 }
 
+expect class Incomplete {
+    fun foo(): Int
+}
+
 expect fun foo(arg: Int): String
 
 expect val flag: Boolean

idea/testData/multiModuleLineMarker/fromCommonToJvmImpl/jvm/jvm.kt

@@ -2,6 +2,8 @@ actual class <lineMarker>Header</lineMarker> {
     actual fun <lineMarker>foo</lineMarker>() = 42
 }
 
+actual class <lineMarker>Incomplete</lineMarker>
+
 actual fun <lineMarker>foo</lineMarker>(arg: Int) = arg.toString()
 
 actual val <lineMarker>flag</lineMarker> = true