correctly coerce values in StackValue.store() (KT-1397)

#KT-1397 fixed

compiler/testData/codegen/regressions/kt1397.kt

@@ -0,0 +1,12 @@
+import java.util.ArrayList
+
+class IntArrayList(): ArrayList<Int>() {
+    override fun get(index: Int): Int = super.get(index)!!
+}
+
+fun box(): String {
+    val a = IntArrayList()
+    a.add(1)
+    a[0]++
+    return if (a[0] == 2) "OK" else "fail"
+}