[NI] Continue resolution after unstable smart cast on receiver

The old inference cosideres candidates with unstable smartcast on
receiver unsuccessful, therefore another one may be selected.
KT-36264

compiler/testData/diagnostics/tests/smartCasts/varnotnull/unnecessaryWithMap.fir.kt

@@ -1,3 +1,5 @@
+// !WITH_NEW_INFERENCE
+
 fun create(): Map<String, String> = null!!
 
 operator fun <K, V> Map<K, V>.iterator(): Iterator<Map.Entry<K, V>> = null!!