Fix conversion error with new ImGui version #461

Job	Run time
clang-format	7s
Windows MSVC Shared Release	2m 3s
Windows MSVC Shared Debug	1m 28s
Windows MSVC Static Release	2m 45s
Windows MSVC Static Debug	2m 41s
Windows ClangCL Shared Release	4m 10s
Windows ClangCL Shared Debug	2m 45s
Windows ClangCL Static Release	4m 33s
Windows ClangCL Static Debug	4m 21s
Windows Clang Shared Release	2m 12s
Windows Clang Shared Debug	2m 2s
Windows Clang Static Release	2m 35s
Windows Clang Static Debug	2m 23s
Linux GCC Shared Release	1m 3s
Linux GCC Shared Debug	37s
Linux GCC Static Release	1m 14s
Linux GCC Static Debug	1m 3s
Linux Clang Shared Release	59s
Linux Clang Shared Debug	47s
Linux Clang Static Release	1m 22s
Linux Clang Static Debug	1m 11s
macOS Clang Shared Release	1m 27s
macOS Clang Shared Debug	55s
macOS Clang Static Release	56s
macOS Clang Static Debug	52s
	46m 31s

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