Integer overflow in delta encoding in `__get`

[springmeyer]

More poking around carmen with an -fsanitize=undefined binary of carmen-cache has revealed a potential overflow. No idea yet if this is harmless, spurious, or an actual problem.

node ./scripts/carmen-analyze.js tiles/01-ne.country.mbtiles
Analyzing tiles/01-ne.country.mbtiles ...
../src/binding.cpp:122:43: runtime error: unsigned integer overflow: 5498430554125 - 6048152813581 cannot be represented in type 'unsigned long long'
SUMMARY: AddressSanitizer: undefined-behavior ../src/binding.cpp:122:43 in 
{ total: 5126,
  degen: 3407,
  ender: 1719,
  byScore: 
   { '0': 534,
     '1': 279,
     '2': 298,
     '3': 325,
     '4': 431,
     '5': 627,
     '6': 756,
     '7': NaN },
  byRelev: 
   { '0.4': 271,
     '0.6': 0,
     '0.8': 0,
     '1.0': 0,
     '1638.6': NaN,
     '1638.4': NaN,
     '1638.2': NaN,
     '1638.0': NaN,
     '1637.8': NaN,
     '1637.6': NaN,
     '1637.4': NaN,
     '1637.2': NaN,
     '1637.0': NaN } }

at

carmen-cache/src/binding.cpp

Line 122 in bd529ff

lastval = lastval - *it;

[springmeyer]

same next action as #75 (comment)

[springmeyer]

presume this was fixed by #116