Memory functions: Improve style.

`try_malloc` was changed in 8bb2c2c0742c57150655e18cf8418a758cebdce8 to
avoid a warning when size is 0.

Code style was also improved on suggestion by @aktau.
This just applies the same style improvements to other similar
functions, to keep code homogeneous.
My first option here was `effective_size` / `effective_count`, but it was a bit long, so I opted for `real_size` / `real_count`. `allocated_size` / `allocated_count` was another option.

To me, any of those are better because they introduce a clear concept. There is a "requested" size and a "real / effective / allocated" size. The fact that difference is being 1 or something else is secondary to that concept. Under this considerations:
```calloc(real_size, real_count)```
reads better to me than
```calloc(size_or_1, count_or_1)```

But this kind of things are very subjective.
I don't have problems to changing names to whatever agreed.
Note that these are very short functions, perfectly understandable anyway.