KT-14209 for loop to stdlib: sum is not recognized if before was check for type

#KT-14209 Fixed

idea/testData/intentions/loopToCallChain/sum/smartCastNotNull.kt

@@ -0,0 +1,9 @@
+// WITH_RUNTIME
+// INTENTION_TEXT: "Replace with 'filterNotNull().sum()'"
+// INTENTION_TEXT_2: "Replace with 'asSequence().filterNotNull().sum()'"
+fun foo(list: List<Int?>){
+    var result = 0
+    <caret>for (l in list)
+        if (l != null)
+            result += l
+}