Fixed fuzzing bugs in signing #639

Job	Run time
build (ubuntu-24.04, x64-linux, gcc, ubuntu-24.04, Unix Makefiles)	14s
build (ubuntu-22.04, x64-linux, gcc, ubuntu-22.04, Unix Makefiles)	16s
build (ubuntu-20.04, x64-linux, gcc, ubuntu-20.04, Unix Makefiles)	19s
build (macOS, x64-osx, clang, macOS-latest, Unix Makefiles, /usr/local/share/vcpkg, /Users/runner...	5m 10s
build (windows-x64-vs, x64-windows, vs, x64, windows-latest, Ninja, C:/vcpkg, C:/Users/runneradmi...	2m 13s
build (windows-x86-vs, x86-windows, vs, x86, windows-latest, Ninja, C:/vcpkg, C:/Users/runneradmi...	2m 23s
build (windows-x64-static-vs, x64-windows-static, vs, x64, windows-latest, Ninja, C:/vcpkg, C:/Us...	2m 54s
build (windows-x64-mingw, x64-windows, mingw, windows-latest, Ninja, C:/vcpkg, C:/Users/runneradm...	3m 3s
	16m 32s

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