Fix compilation error if expression length != message length #476

Job	Run time
Install Ubuntu GCC static Release	13s
Install Ubuntu GCC header-only Release	15s
Install Ubuntu GCC shared Release	13s
Ubuntu GCC Release	1m 48s
Ubuntu GCC Debug	52s
Ubuntu GCC noexcept Release	52s
Ubuntu GCC noexcept Debug	42s
Ubuntu GCC notime Release	1m 7s
Ubuntu GCC notime Debug	42s
Ubuntu GCC nounity Release	1m 10s
Ubuntu GCC nounity Debug	47s
Ubuntu GCC header-only Release	1m 23s
Ubuntu GCC header-only Debug	46s
Ubuntu GCC shared Release	1m 22s
Ubuntu GCC shared Debug	41s
Ubuntu Clang Release	1m 8s
Ubuntu Clang Debug	48s
Ubuntu Clang noexcept Release	58s
Ubuntu Clang noexcept Debug	46s
Windows 32 Release	2m 25s
Windows 32 Debug	1m 32s
Windows 64 Release	2m 42s
Windows 64 Debug	1m 23s
Windows 64 noexcept Release	2m 55s
Windows 64 noexcept Debug	1m 18s
Windows 64 shared Release	3m 6s
Windows 64 shared Debug	1m 47s
MacOS Release	37s
MacOS Debug	28s
MacOS noexcept Release	30s
MacOS noexcept Debug	34s
WebAssembly Release	3m 21s
WebAssembly Debug	1m 33s
WebAssembly noexcept Release	1m 10s
WebAssembly noexcept Debug	55s
	42m 49s

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