BUG: specfun/specfun.h: initialize kd in mtu12 to fix potential uninitialized use

[stratakis]

The kd variable was not initialized before the kf==1/kf==2 conditional blocks. If kf had an unexpected value, kd would be used uninitialized when passed to cva2(). Initialize to 0 for consistency with mtu0.

Uncovered by Coverity static analysis.

[stratakis]

This is not trigerrable with the current callers as kf will always be 1 or 2. However mtu12() is a public template function and future callers could potentially pass invalid values.

Coverity message

1. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:4762:9: var_decl: Declaring variable "kd" without initializer.
2. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:4764:9: path: Condition "kf == 1", taking false branch.
3. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:4767:9: path: Condition "kf == 1", taking false branch.
4. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:4770:9: path: Condition "kf == 2", taking false branch.
5. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:4773:9: path: Condition "kf == 2", taking false branch.
**6. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:4777:9: uninit_use_in_call: Using uninitialized value "kd" when calling "cva2".**
7. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1737:9: path: Condition "m <= 12", taking true branch.
8. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1738:13: read_value: Reading value "kd" when calling "cv0".
9. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1590:9: path: Condition "m == 0", taking true branch.
10. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1591:13: path: Condition "q <= 1.", taking false branch.
11. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1593:20: path: Condition "q <= 10.", taking false branch.
12. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1596:17: read_value: Reading value "kd" when calling "cvql".
13. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1866:9: read_value: Reading value "kd".
14. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1866:9: path: Condition "kd == 1", taking true branch.
15. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1869:9: path: Condition "kd == 3", taking false branch.
16. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1869:9: path: Condition "kd == 4", taking false branch.
17. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1598:9: path: Falling through to end of if statement.
18. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1739:13: path: Condition "q != 0.", taking true branch.
19. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1739:13: path: Condition "m != 2", taking true branch.
20. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1742:13: path: Condition "q > 0.002", taking true branch.
21. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1742:13: path: Condition "m == 2", taking false branch.
22. scipy-1.16.2/subprojects/xsf/include/xsf/specfun/specfun.h:1745:9: path: Falling through to end of if statement.
# 4775| }
# 4776|
# 4777|-> a = cva2(kd, m, q);
# 4778|
# 4779| if (q <= 1.0) {