[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/tests/smartCasts/ifExprInWhenSubjectNonNull.fir.kt

@@ -0,0 +1,11 @@
+fun baz(s: String?, u: String?): String {
+    val t = when(if (u == null) return "" else u) {
+        "abc" -> u
+        "" -> {
+            if (s == null) return ""
+            s
+        }
+        else -> u
+    }
+    return t
+}