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

this will silence a lot of static code analysis warnings

src/angle.cpp

@@ -351,7 +351,7 @@ void Angle::ev_tally(int i, int j, int k, int nlocal, int newton_bond,
 double Angle::memory_usage()
 {
   double bytes = comm->nthreads*maxeatom * sizeof(double);
-  bytes += comm->nthreads*maxvatom*6 * sizeof(double);
-  bytes += comm->nthreads*maxcvatom*9 * sizeof(double);
+  bytes += (double)comm->nthreads*maxvatom*6 * sizeof(double);
+  bytes += (double)comm->nthreads*maxcvatom*9 * sizeof(double);
   return bytes;
 }