Fix fallback logic in `analysis.getPositionContext`

[llogick]

Most lines are indented, ie line[0] == ' '(a space).

Tokenizing line as the sole buffer returns location offsets relative/within to that line, but are expected to be indexes within handle.tree.source .

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6478f1a) 76.58% compared to head (b4d49a9) 76.59%.

Files	Patch %	Lines
src/analysis.zig	90.00%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1754   +/-   ##
=======================================
  Coverage   76.58%   76.59%           
=======================================
  Files          35       35           
  Lines       10088    10090    +2     
=======================================
+ Hits         7726     7728    +2     
  Misses       2362     2362           

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[llogick]

Having done this makes me realize having that logic is very dicey and https://github.com/zigtools/zls/blob/05ae41e3f4af684628c97a921b85e07d921f38e2/src/features/completions.zig#L1338 should just use tok_loc.end or https://github.com/zigtools/zls/blob/05ae41e3f4af684628c97a921b85e07d921f38e2/src/features/completions.zig#L1197 look_ahead = true here (haven't tested for side effects).

[llogick]

This is a low priority PR, the test changes are worth having, but in my opinion the fallback logic shouldn't exist (and obviously nothing depends on it currently).