FIR: strengthen resolution success check for augmented array set call

This commit removes some false ambiguities &
fixes compilation of tree-generator module with FIR

compiler/testData/ir/irText/expressions/lambdaInCAO.fir.kt.txt

@@ -16,7 +16,14 @@ fun test1(a: Any) {
 }
 
 fun test2(a: Any) {
-  error("") /* ErrorCallExpression */
+  { // BLOCK
+    val <<array>>: Any = a
+    val <<index_0>>: Function0<Unit> = local fun <anonymous>() {
+      return Unit
+    }
+
+    <<array>>.set(index = <<index_0>>, value = <<array>>.get(index = <<index_0>>).plus(other = 42))
+  }
 }
 
 fun test3(a: Any) {