Fix default value generation after suspension point

Replace coercion from VOID with call 'pushDefaultValueOnStack'

It's necessary because coercion of VOID to java/lang/Object ends with Unit instance on stack
that makes variables spilling algorithm thinking that variable is Unit

 #KT-13409 Fixed

compiler/testData/codegen/box/coroutines/falseUnitCoercion.kt

@@ -0,0 +1,24 @@
+class Controller {
+    suspend fun <T> suspendHere(v: T, x: Continuation<T>) {
+        x.resume(v)
+    }
+}
+
+fun builder(coroutine c: Controller.() -> Continuation<Unit>) {
+    c(Controller()).resume(Unit)
+}
+
+var result: Any = ""
+
+fun <T : Any> foo(v: T) {
+    builder {
+        val r = suspendHere(v)
+        suspendHere("")
+        result = r
+    }
+}
+
+fun box(): String {
+    foo("OK")
+    return result as String
+}