fix: out-of-bounds write in decimal Display implementation
fixes #71 (closed) (more details in the comment).
Previously we used ds->digits+14
buffer capacity to display a
decimal with decNumberToString() function, while Tarantool uses
DECIMAL_MAX_DIGITS + 14
length. As a result we have faced malloc
header corruption in its free block list caused by an out of bounds
write to buffer (other possible result could be a memory segfault).
Edited by Denis Smirnov