[Bug] SEGV occurs in parameter initialization behaviour.

I found a bug that causes SEGV in CKKS mode. 
The MWE is as follows:
```c++
#include <helib/helib.h>

using namespace std;
using namespace helib;

Context context = ContextBuilder<CKKS>()
.m(1024)
.precision(20)
.scale(4)
.bits(150)
.c(2)
.build();


int main(int argc, char* argv[])
{
    return 0;
}
```