[FileFormats.LP] Fix edge case handling of quadratic open/close brackets

[odow]

Closes #2040
Closes #2041
Closes #2043

I wish there was a standard for the LP file format...

1703 has

  + 2.28 x58 * x61 - 1.12 x59^2 + 0.08 x59 * x60 - 0.64 x59 * x61 - 1.74 x60^2 - 1.36 x60 * x61 + 1.44 x61^2 
  ]/2

and

- 0.94 x52 - 0.33 x53 - 0.07 x54 + 0.16 x55 + 0.71 x56 - 0.9 x57 - 0.86 x58 - 0.17 x59 - 0.16 x60 - 0.56 x61
+ [ 0.13 x2^2 - 1.72 x2 * x3 - 1.94 x2 * x4 - 0.58 x2 * x5 + 1.32 x2 * x6 + 1.82 x2 * x7 + 1.68 x2 * x8 
+ 1.56 x2 * x9 - 0.92 x2 * x10 - 1.88 x2 * x11 - 0.68 x2 * x12 + 0.28 x2 * x13 - 0.66 x2 * x14 - 1.96 x2 * x15 

...

- 0.84 x53 - 0.84 x54 - 0.91 x55 + 0.24 x56 + 0.19 x57 - 0.92 x58 - 0.4 x59 - 0.68 x60 + 0.93 x61 + 
[ - 0.84 x2^2 - 0.72 x2 * x3 - 1.98 x2 * x4 - 0.74 x2 * x5 + 1.32 x2 * x6 + 1.14 x2 * x7 + 0.08 x2 * x8 
-

3913 has:

  - 0.4672975212 b299 * b301 + 14.146305564 b300^2 - 0.3698311256 b300 * b301 + 14.344640362 b301^2 ]
  /2