pixbuf bounds adjustments do weird things

[georgevdd]

Expected behavior

Negative and out-of-bounds indices to pixbuf.buffer:sub() and related methods (replace(), shift(), map()) should raise errors if not supported, or else behave analogously to indices given to string.sub(). (Documentation for buffer.sub() explicitly draws this comparison.)

Actual behavior

> pixbuf=require'pixbuf'
> buf = pixbuf.newBuffer(4, 4)
> buf:set(1, 'AAAABBBBCCCCDDDD')
> print(('>>%s<<'):format(('ABCD'):sub(5, -1)))
>><<
> print(('>>%s<<'):format(buf:sub(5, -1):dump()))  -- should be empty too
>>DDDD<<

> buf:replace('XXXX', 5)  -- off the end
> print(buf:dump())
AAAABBBBCCCCXXXX

> buf:map(function(r, g, b, w) return r+1, g+1, b+1, w+1 end, buf, -1, -1) -- just the last pixel
Lua error:      stdin:1: bad argument #2 to 'map' (Buffer limits out of order)
stack traceback:
        [C]: in function 'map'
        stdin:1: in main chunk
        [C]: ?
        [C]: ?

> buf:shift(1, pixbuf.SHIFT_LOGICAL, 5, 5)  -- off the end
> print(('>>%s<<'):format(buf:dump()))
>>AAAABBBBCCCC<<

Test code

pixbuf=require'pixbuf'
buf = pixbuf.newBuffer(4, 4)
buf:set(1, 'AAAABBBBCCCCDDDD')
print(('>>%s<<'):format(('ABCD'):sub(5, -1)))
print(('>>%s<<'):format(buf:sub(5, -1):dump()))  -- should be empty too

buf:replace('XXXX', 5)  -- off the end
print(buf:dump())

buf:map(function(r, g, b, w) return r+1, g+1, b+1, w+1 end, buf, -1, -1) -- just the last pixel

buf:shift(1, pixbuf.SHIFT_LOGICAL, 5, 5)  -- off the end
print(('>>%s<<'):format(buf:dump()))

NodeMCU startup banner

NodeMCU 3.0.0.0 
        branch: fixbuf-base
        commit: 0661fe100172a6a1b724488abcbdaefc854dc267
        release: 3.0.0-release_20211229 +58
        release DTS: 202604111201
        SSL: false
        build type: float
        LFS: 0x20000 bytes total capacity
        modules: bit,color_utils,file,gpio,http,net,node,pixbuf,tmr,uart,wifi,ws2812

Hardware

Adafruit Feather Huzzah + no special hardware.