Merge branch 'bugfix/kostyantyn/mmodel-initializers' into 'master'

Bugfix in memory model initialization

The E-ACSL instrumentation engine does instrument `__e_acsl_memory_init` function (which initializes a memory model) if there are no variables to track. This is a shortcoming because a program might still need to track its memory state, for instance the following program: 

```
int main(void) {
    /* Allocation increases */
    char *a = malloc(7);
    /* @assert (__heap_size == 7);  */
}
``` 
This merge request suggests a fix for this issue.


See merge request !42