Fix removed tgamma error handling path

[mborland]

Closes: #1194

Confirmed on device: https://github.com/cppalliance/cuda-math/pull/24

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.93939% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.79%. Comparing base (cb06899) to head (9d13307). Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
include/boost/math/special_functions/gamma.hpp	87.50%	2 Missing :warning:

Additional details and impacted files

[](https://app.codecov.io/gh/boostorg/math/pull/1195?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) ```diff @@ Coverage Diff @@ ## develop #1195 +/- ## ======================================== Coverage 93.78% 93.79% ======================================== Files 655 656 +1 Lines 53783 53804 +21 ======================================== + Hits 50440 50464 +24 + Misses 3343 3340 -3 ``` | [Files with missing lines](https://app.codecov.io/gh/boostorg/math/pull/1195?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) | Coverage Δ | | |---|---|---| | [test/git\_issue\_1194.cpp](https://app.codecov.io/gh/boostorg/math/pull/1195?src=pr&el=tree&filepath=test%2Fgit_issue_1194.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-dGVzdC9naXRfaXNzdWVfMTE5NC5jcHA=) | `100.00% <100.00%> (ø)` | | | [include/boost/math/special\_functions/gamma.hpp](https://app.codecov.io/gh/boostorg/math/pull/1195?src=pr&el=tree&filepath=include%2Fboost%2Fmath%2Fspecial_functions%2Fgamma.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-aW5jbHVkZS9ib29zdC9tYXRoL3NwZWNpYWxfZnVuY3Rpb25zL2dhbW1hLmhwcA==) | `92.14% <87.50%> (+0.04%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/boostorg/math/pull/1195/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/boostorg/math/pull/1195?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/boostorg/math/pull/1195?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Last update [cb06899...9d13307](https://app.codecov.io/gh/boostorg/math/pull/1195?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg).