Fix T78415: Particle Edit mode Add brush with a radius > 181px crashes

Caused by short overflow, change to int instead.

Maniphest Tasks: T78415

Differential Revision: https://developer.blender.org/D8148

source/blender/editors/physics/particle_edit.c

@@ -4103,7 +4103,7 @@ static void brush_add_count_iter(void *__restrict iter_data_v,
   BrushAddCountIterTLSData *tls = tls_v->userdata_chunk;
   const int number = iter_data->number;
   const short size = iter_data->size;
-  const short size2 = size * size;
+  const int size2 = size * size;
   float dmx, dmy;
   if (number > 1) {
     dmx = size;