Fix substitute newline: Memory functions: Improve style.

`try_malloc` was changed in 8bb2c2c0742c57150655e18cf8418a758cebdce8 to
avoid a warning when size is 0. Then, this improves some things on that:

- Use local vars instead of changing parameters.
- Homogenize style for other related functions.
Merge pull request #1526 from elmart/mem-func-impr

Memory functions: Improve style.