add typecast to avoid (unlikely but possible) integer overflows.

this will silence a lot of static code analysis warnings

src/compute_temp_profile.cpp

@@ -578,6 +578,6 @@ void ComputeTempProfile::bin_assign()
 double ComputeTempProfile::memory_usage()
 {
   double bytes = maxatom * sizeof(int);
-  bytes += nbins*ncount * sizeof(double);
+  bytes += (double)nbins*ncount * sizeof(double);
   return bytes;
 }