Reported by clang-tidy (seen on Linux with v18, v19, v20, not on macOS):
```
tests/server/dnsd.c:552:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/dnsd.c:556:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/rtspd.c:1183:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/rtspd.c:1187:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/sws.c:2235:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/sws.c:2239:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/tftpd.c:1188:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/tftpd.c:1192:14: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/util.c:860:21: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
tests/server/util.c:864:21: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
```
Ref: https://github.com/curl/curl/actions/runs/22424827575/job/64930560425?pr=20725
Cherry-picked from #20725Closes#20730