[NI] Fix exception, recorded type for function statement can be null

See `checkStatementType`, we return `null` to reduce count of errors.

 Also, note that named function which is used as last statement in lambda
 doesn't coerce to Unit, this is a separate bug and will be addressed later,
 see #KT-25383

 #EA-121026 Fixed

compiler/testData/diagnostics/tests/inference/localFunctionInsideIfBlock.kt

@@ -0,0 +1,10 @@
+// !LANGUAGE: +NewInference
+
+fun bar() {
+    if (true) <!TYPE_MISMATCH!>{
+        <!EXPECTED_TYPE_MISMATCH!>fun local() {
+        }<!>
+    }<!> else {
+
+    }
+}