Fix some errors which didn't trigger a break loop anymore

[fingolfin]

Specifically use ErrorMayQuit instead of ErrorQuit in CheckIsPossList and
CheckIsDenseList to ensure this produces a break loop again:

f:=function()
local a,v;
  a:=[1.2,3];
  v:=2;
  v:=a{v};
end;
f();

Fixes #3011

I suggest to backport this to stable-4.10

[hulpke]

I approve of this being fixed but don't know enough about the kernel to say whether it is the right way.

[markuspf]

This is exactly the fix I intended to fix #2920

[codecov]

Codecov Report

Merging #3013 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3013      +/-   ##
==========================================
- Coverage   85.14%   85.14%   -0.01%     
==========================================
  Files         112      112              
  Lines       56959    56959              
==========================================
- Hits        48497    48495       -2     
- Misses       8462     8464       +2

Impacted Files	Coverage Δ
src/error.c	79.61% <100%> (ø)	⬆️
src/saveload.c	66.04% <0%> (-0.54%)	⬇️