overflow in shift_line

Date: 16.11.2023
Severity: Low

When shifting lines in operator pending mode and using a very large
value, we may overflow the size of integer. Fix this by using a long long
variable, testing if the result would be larger than INT_MAX and if so,
indent by INT_MAX value.

Impact is low, user interaction is required and a crash may not even happen.

The Vim project would like to thank Fabian Toepfer for reporting this issue
which is now fixed in Vim patch 9.0.2112.