Fix for KT-14868: CCE in runtime while converting Number to Char

#KT-14868 Fixed

compiler/testData/codegen/box/primitiveTypes/kt14868.kt

@@ -0,0 +1,6 @@
+
+fun box(): String {
+    val x: Number = 75
+
+    return "O" + x.toChar()
+}

compiler/testData/codegen/light-analysis/primitiveTypes/kt14868.txt

@@ -0,0 +1,3 @@
+public final class Kt14868Kt {
+    public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
+}