ensure `quit` on config error with `IOError` (#5011)

When there is an `IOError` while logging a configuration error,
we don't actually `quit` the program. Catch `IOError` to always `quit`.

beacon_chain/nimbus_binary_common.nim

@@ -208,6 +208,7 @@ template makeBannerAndConfig*(clientId: string, ConfType: type): untyped =
     )
   except CatchableError as err:
     # We need to log to stderr here, because logging hasn't been configured yet
+    try:
       stderr.write "Failure while loading the configuration:\n"
       stderr.write err.msg
       stderr.write "\n"
@@ -221,6 +222,8 @@ template makeBannerAndConfig*(clientId: string, ConfType: type): untyped =
           stderr.write "Since the '" & fieldName & "' option is allowed to " &
                        "have more than one value, please make sure to supply " &
                        "a properly formatted TOML array\n"
+    except IOError:
+      discard
     quit 1
   {.pop.}
   config