more typecasts to double to avoid 32-bit int overflows when computing memory usage

src/pair_hybrid.cpp

@@ -1078,7 +1078,7 @@ int PairHybrid::check_ijtype(int itype, int jtype, char *substyle)
 
 double PairHybrid::memory_usage()
 {
-  double bytes = maxeatom * sizeof(double);
+  double bytes = (double)maxeatom * sizeof(double);
   bytes += (double)maxvatom*6 * sizeof(double);
   bytes += (double)maxcvatom*9 * sizeof(double);
   for (int m = 0; m < nstyles; m++) bytes += styles[m]->memory_usage();