table_ensure_space

Makes sure items more entries can be added without the table growing again.

Does nothing when there is room. When many removed entries fill the table, it rehashes at the size the live entries need instead of doubling. table_add calls it with 1; call it with a larger number before a bulk add to avoid repeated growth. A negative items fails an assert.

table: Table(int, int);
table_ensure_space(*table, 500);
slots := table.allocated;
for 0..499 table_add(*table, it, it);
assert(table.allocated == slots);
deinit(*table);

table_ensure_space :: (table: *Table, items: s64)