Fix compilation error if expression length != message length #472

Job	Run time
Install Ubuntu GCC static Release	32s
Install Ubuntu GCC header-only Release	18s
Install Ubuntu GCC shared Release	18s
Ubuntu GCC Release	1m 46s
Ubuntu GCC Debug	1m 24s
Ubuntu GCC noexcept Release	59s
Ubuntu GCC noexcept Debug	46s
Ubuntu GCC notime Release	1m 14s
Ubuntu GCC notime Debug	51s
Ubuntu GCC nounity Release	1m 20s
Ubuntu GCC nounity Debug	50s
Ubuntu GCC header-only Release	1m 24s
Ubuntu GCC header-only Debug	42s
Ubuntu GCC shared Release	1m 12s
Ubuntu GCC shared Debug	43s
Ubuntu Clang Release	1m 16s
Ubuntu Clang Debug	49s
Ubuntu Clang noexcept Release	1m 16s
Ubuntu Clang noexcept Debug	46s
Windows 32 Release	2m 44s
Windows 32 Debug	1m 24s
Windows 64 Release	2m 45s
Windows 64 Debug	1m 37s
Windows 64 noexcept Release	2m 43s
Windows 64 noexcept Debug	1m 47s
Windows 64 shared Release	2m 38s
Windows 64 shared Debug	1m 27s
MacOS Release	40s
MacOS Debug	32s
MacOS noexcept Release	39s
MacOS noexcept Debug	31s
WebAssembly Release	3m 13s
WebAssembly Debug	1m 23s
WebAssembly noexcept Release	1m 30s
WebAssembly noexcept Debug	58s
	44m 57s

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