MSVC: tidy up type conversion warnings

dev/standalone/mchiter.c

@@ -1833,7 +1833,7 @@ int create_mchiterbufs(double maxpscat,dataptr dz)
     }
     dz->buflen     = (int)(bigbufsize/sizeof(float));
     big_buffer_size = dz->buflen + extra_space;
-    if((dz->bigbuf = (float *) Malloc(big_buffer_size * sizeof(float)))==NULL) {
+    if((dz->bigbuf = (float *) Malloc((long)(big_buffer_size * sizeof(float))))==NULL) {
         sprintf(errstr, "INSUFFICIENT MEMORY to create sound buffers.\n");
         return(MEMORY_ERROR);
     }