Do not show warning about useless elvis for error function types

#KT-17214 Fixed
 #KT-12112 Fixed

compiler/testData/diagnostics/tests/nullableTypes/uselessElvis.kt

@@ -35,10 +35,14 @@ fun test() {
         takeNotNull(dependOn(dependOn(x)) <!USELESS_ELVIS!>?: ""<!>)
         takeNotNull(dependOn(dependOn(x) <!USELESS_CAST!>as? String<!>) ?: "")
     }
+
+    takeNotNull(bar()!!)
 }
 
 inline fun <reified T : Any> reifiedNull(): T? = null
 
 fun testFrom13648() {
     takeNotNull(reifiedNull() ?: "")
-}
+}
+
+fun bar() = <!UNRESOLVED_REFERENCE!>unresolved<!>

compiler/testData/diagnostics/tests/nullableTypes/uselessElvis.txt

@@ -1,5 +1,6 @@
 package
 
+public fun bar(): [ERROR : Error function type]
 public fun </*0*/ T> dependOn(/*0*/ x: T): T
 public fun </*0*/ T> notNull(): T
 public fun </*0*/ T> nullable(): T?

compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/elvis.kt

@@ -61,6 +61,7 @@ fun test() {
     takeNotNull(J.getNAny() ?: J())
 
     val x = <!UNRESOLVED_REFERENCE!>unresolved<!> ?: null
+    <!UNREACHABLE_CODE!>val y =<!> <!UNRESOLVED_REFERENCE!>unresolved<!>.<!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>foo<!> ?: return
 }
 
 fun takeNotNull(s: J) {}