Fix safe calls codegen for nullable generic

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

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

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

@@ -0,0 +1,8 @@
+fun Int.foo() = 239
+fun Long.bar() = 239.toLong()
+
+fun box(): String {
+    42?.foo()
+    42.toLong()?.bar()
+    return "OK"
+}