Cleanup various varargs shenanigans (#9624)

* Iterate over varargs directly via select if possible
* Use table.pack otherwise (https://github.com/koreader/koreader-base/pull/1535).
* This allows us to simplify a few Logger calls, as logger now handles nil values.

.luacheckrc

@@ -6,6 +6,8 @@ self = false
 globals = {
     "G_reader_settings",
     "G_defaults",
+    "table.pack",
+    "table.unpack",
 }
 
 read_globals = {