FocusSerial: isEOL() should return true when there's no more data

We should be treating the end of data the same way we treat a newline.

A common issue that affects a good number of plugins is that we don't deal with
trailing space well. For example, most plugins that respond with a large list of
values, where we iterate over an array or list, or something else, they usually
end up responding with a trailing space before the newline.

If we feed that same string back as an update, we can end up in a situation
where we lock up (or become very, very slow), because we want to read more data
than is available. Why? Because `Serial.parseInt()` (used by Focus under the
hood) will swallow up any leading whitespace. So if we have "255 \n" as an
argument list, we'll parse the first number, and the second `parseInt()` will
return 0, because it times out waiting for a number, consuming both the space
and the newline in the process. Thus, the next `::isEOL()` will still return
false, because `peek()` returns `-1`, signaling no data.

That can confuse the heck out of our plugins. To combat that, we should treat
end of data the same as EOL, and return false if `peek()` returns -1, too.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

plugins/Kaleidoscope-FocusSerial/src/kaleidoscope/plugin/FocusSerial.h

@@ -104,7 +104,9 @@ class FocusSerial : public kaleidoscope::Plugin {
   }
 
   bool isEOL() {
-    return Runtime.serialPort().peek() == NEWLINE;
+    int i = Runtime.serialPort().peek();
+
+    return (i == NEWLINE || i == -1);
   }