KT-10706: do not report IMPLICIT_CAST_TO_ANY on expressions of type Nothing

compiler/testData/diagnostics/tests/controlStructures/kt10706.kt

@@ -0,0 +1,12 @@
+fun TODO(): Nothing = null!!
+
+fun fn(c: Char?): Any? =
+        if (c == null) TODO()
+        else when (<!DEBUG_INFO_SMARTCAST!>c<!>) {
+            'a' -> when (<!DEBUG_INFO_SMARTCAST!>c<!>) {
+                'B' -> <!IMPLICIT_CAST_TO_ANY!>1<!>
+                'C' -> <!IMPLICIT_CAST_TO_ANY!>"sdf"<!>
+                else -> TODO()
+            }
+            else -> TODO()
+        }

compiler/testData/diagnostics/tests/controlStructures/kt10706.txt

@@ -0,0 +1,4 @@
+package
+
+public fun TODO(): kotlin.Nothing
+public fun fn(/*0*/ c: kotlin.Char?): kotlin.Any?