Disable use of flashbangs on robots

Flashbangs could blind and stun turrets and other robots.
In real life, flashbangs have no effect on robots. Prevent them from
having an effect in game.

src/explosion.cpp

@@ -61,6 +61,7 @@
 #include "type_id.h"
 
 static const itype_id null_itype( "null" );
+static const species_id ROBOT( "ROBOT" );
 
 // Global to smuggle data into shrapnel_calc() function without replicating it across entire map.
 // Mass in kg
@@ -550,6 +551,9 @@ void flashbang( const tripoint &p, bool player_immune )
         }
     }
     for( monster &critter : g->all_monsters() ) {
+        if( critter.type->in_species( ROBOT ) ) {
+            continue;
+        }
         // TODO: can the following code be called for all types of creatures
         dist = rl_dist( critter.pos(), p );
         if( dist <= 8 ) {