Divide by zero with getmousepos() and 'smoothscroll' #16732

Job	Run time
linux (tiny, clang, native)	2m 33s
linux (tiny, gcc, native)	2m 18s
macos (tiny, macos-12)	1m 10s
linux (normal, clang, native)	3m 30s
linux (normal, gcc, native)	3m 28s
macos (tiny, macos-14)	40s
linux (huge, clang, native)	3m 17s
macos (normal, macos-12)	3m 28s
linux (huge, gcc, native)	3m 30s
macos (normal, macos-14)	1m 1s
linux (tiny, clang, nogui)	2m 23s
macos (huge, macos-12)	3m 27s
linux (tiny, gcc, nogui)	2m 36s
macos (huge, macos-14)	3m 31s
linux (normal, gcc, i386, ./src/shadow)	3m 17s
linux (huge, gcc, uchar, testgui, true, dynamic)	3m 32s
windows (HUGE, msvc, no, no, x64, stable)	55s
windows (HUGE, mingw, yes, yes, x86, stable, yes)	1m 10s
linux (huge, clang, asan, 5.1)	3m 30s
windows (HUGE, msvc, no, yes, x86)	51s
linux (huge, gcc, unittests, true)	3m 6s
windows (HUGE, mingw, yes, no, x64, yes)	1m 52s
linux (normal, gcc, vimtags)	2m 41s
windows (NORMAL, msvc, yes, no, x86)	37s
windows (NORMAL, mingw, no, yes, x64)	34s
windows (TINY, msvc, yes, yes, x64)	1s
windows (TINY, mingw, no, no, x86)	22s
	59m 20s

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