cc1: warnings being treated as errors
  libs/esl/src/esl.c: In function "esl_recv_event":
  libs/esl/src/esl.c:1190: error: array subscript is above array bounds
  libs/esl/src/esl.c:1227: error: array subscript is above array bounds

Clamp handle_recv() return value to safe values.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>