[BUG] Null optional completion times raise TypeError in JSONResultParser #60

Describe the bug

JSONResultParser.parse_json_element() checks whether completion-time keys exist, but then divides their values by 3600 without checking for None. Its comment says to calculate only when the value is not None; a synthetic comp_main: null instead raises TypeError.

To Reproduce

Without making any request:

from howlongtobeatpy.JSONResultParser import JSONResultParser
p = JSONResultParser('Example', 'https://example.com', 0)
p.parse_json_element({'game_id': 1, 'game_name': 'Example', 'comp_main': None})
# TypeError: unsupported operand type(s) for /: 'NoneType' and 'int'

I loaded the parser and its entry class from the checkout for this local test, without loading the HTTP implementation. Control inputs comp_main=0 and comp_main=3600 yield 0.0 and 1.0 respectively.

Expected behavior

Treat a null optional completion time as unavailable, keeping the entry field None, while preserving zero and ordinary numeric values. Apply the same handling to the other optional time fields (comp_plus, comp_100, comp_all, invested_co, invested_mp).

HLTB API Version

Current repository source, Python 3.14.6, macOS arm64. This is a synthetic parser robustness reproduction, not a claim that I captured a current live API response containing null values.

This is separate from search discovery / bot-protection reports and the platform accessor issue. Existing issues and open PRs were checked. Happy to contribute a focused parser regression/fix if accepted. AI assistance was used; output reproduced locally.