buffering issue with final NECRepeatIRMessage in NonblockingGenericDecode read method

In running the irremote_nonblocking.py (I modified it to use a .5 second heartbeat) I see the following. If you notice, holding down the key on the IR remote sends a code followed by a number of NECRepeatIRMessage. However, I can stop pressing on a key, and wait a couple seconds and press a different key, and out pops one last NECRepeatIRMessage before the next decoded key.

I suspect that the pulse buffer has one last repeat message that it's received but doesn't provide until the something else arrives in the pulse buffer to flush it out. In testing it seems like virtually every key in my remote generates at least one NECRepeatIRMessage, but it doesn't arrive until the next key is pressed, possibly minutes later.

`t=8.02 Heartbeat
t=8.06 New Message
Heard 67 Pulses: (8927, 4487, 546, 606, 524, 576, 551, 576, 521, 606, 524, 576, 551, 575, 521, 583, 547, 576, 549, 1704, 525, 1702, 521, 1706, 551, 1703, 523, 1681, 544, 1704, 550, 1679, 549, 1679, 546, 580, 548, 1678, 546, 1681, 575, 550, 548, 579, 550, 549, 577, 1676, 575, 526, 600, 1653, 573, 527, 576, 550, 549, 1679, 576, 1677, 549, 1677, 549, 578, 574, 1652, 549)
Decoded: (255, 0, 157, 98)
----------------------------
t=8.16 New Message
Heard 3 Pulses: (8931, 2256, 549)
NEC repeat!
----------------------------
t=8.26 New Message
Heard 3 Pulses: (8929, 2283, 527)
NEC repeat!
----------------------------
t=8.37 New Message
Heard 3 Pulses: (8934, 2254, 549)
NEC repeat!
----------------------------
t=8.48 New Message
Heard 3 Pulses: (8929, 2257, 548)
NEC repeat!
----------------------------
t=8.52 Heartbeat
t=8.59 New Message
Heard 3 Pulses: (8929, 2256, 548)
NEC repeat!
----------------------------
t=8.69 New Message
Heard 3 Pulses: (8931, 2256, 549)
NEC repeat!
----------------------------
t=8.8 New Message
Heard 3 Pulses: (8932, 2255, 549)
NEC repeat!
----------------------------
t=8.91 New Message
Heard 3 Pulses: (8931, 2255, 549)
NEC repeat!
----------------------------
t=9.02 Heartbeat
t=9.52 Heartbeat
t=10 Heartbeat
t=10.5 Heartbeat
t=10.6 New Message
Heard 3 Pulses: (8905, 2306, 529)
NEC repeat!
----------------------------
t=10.7 New Message
Heard 67 Pulses: (8932, 4484, 522, 630, 525, 575, 552, 575, 498, 628, 526, 574, 552, 575, 519, 608, 525, 575, 550, 1703, 525, 1701, 497, 1730, 552, 1701, 525, 1702, 522, 1705, 550, 1703, 525, 1702, 521, 583, 546, 1680, 546, 1704, 550, 551, 548, 578, 550, 551, 574, 1680, 547, 551, 577, 1679, 547, 551, 599, 526, 550, 1680, 575, 1677, 574, 1652, 549, 578, 550, 1675, 574)
Decoded: (255, 0, 157, 98)
----------------------------
`

Start with irremote_nonblocking.py and the NonblockingGenericDecode read method, then reproduce the reported sequence using the .5 second heartbeat and inspect when the pulse buffer is read or flushed. Done means a final NECRepeatIRMessage is delivered after the key is released rather than being delayed until another key is pressed.

Written by the indexing model from the issue text.