patch 9.0.2108: [security]: overflow with count for :s command

patch 9.0.2108: [security]: overflow with count for :s command

Problem:  [security]: overflow with count for :s command
Solution: Abort the :s command if the count is too large

If the count after the :s command is larger than what fits into a
(signed) long variable, abort with e_value_too_large.

Adds a test with INT_MAX as count and verify it correctly fails.

It seems the return value on Windows using mingw compiler wraps around,
so the initial test using :s/./b/9999999999999999999999999990 doesn't
fail there, since the count is wrapping around several times and finally
is no longer larger than 2147483647. So let's just use 2147483647 in the
test, which hopefully will always cause a failure

Signed-off-by: Christian Brabandt <cb@256bit.org>