Fix elvis expression in case of nullable generic

compiler/testData/codegen/box/elvis/genericNull.kt

@@ -0,0 +1,8 @@
+fun foo<T: Number?>(t: T) {
+    (t ?: 42).toInt()
+}
+
+fun box(): String {
+    foo<Int?>(null)
+    return "OK"
+}

compiler/testData/codegen/box/elvis/primitive.kt

@@ -0,0 +1,6 @@
+fun box(): String {
+    if ((42 ?: 239) != 42) return "Fail Int"
+    if ((42.toLong() ?: 239.toLong()) != 42.toLong()) return "Fail Long"
+    
+    return "OK"
+}