Fix inline classes coercion in 'if' expression

#KT-27132

compiler/testData/codegen/box/inlineClasses/kt27132.kt

@@ -0,0 +1,23 @@
+// !LANGUAGE: +InlineClasses
+// IGNORE_BACKEND: JVM_IR, JS_IR
+// WITH_RUNTIME
+
+inline class Ucn(private val i: UInt)
+
+interface Input<T> {
+    fun foo(n: Int = 0): T
+}
+
+fun Char.toUInt() = toInt().toUInt()
+
+class Kx(val x: UInt) : Input<Ucn> {
+    override fun foo(n: Int): Ucn =
+        if (n < 0) Ucn(0u) else Ucn(x)
+}
+
+fun box(): String {
+    val p = Kx(42u).foo()
+    if (p.toString() != "Ucn(i=42)") throw AssertionError()
+
+    return "OK"
+}