[slang-tidy] Fix UB with unmodified stringstream input argument #1521

Job	Run time
conan	6m 22s
build (clang-sanitize, ubuntu-22.04)	33m 5s
bindings	17m 43s
build (gcc-release, ubuntu-22.04)	7m 39s
linux-coverage	12m 6s
build (gcc-11-release, ubuntu-22.04)	7m 41s
build (gcc-debug-shared, ubuntu-22.04)	6m 39s
build (gcc-debug-noexcept, ubuntu-22.04)	7m 7s
build (macos-release, macos-13)	5m 35s
build (win64-release, windows-latest)	10m 24s
build (win64-debug-shared, windows-latest)	8m 15s
build (win64-debug-noexcept, windows-latest)	7m 29s
	2h 10m 5s

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