[Add] Added a check for negative prices.

src/ship.c

@@ -213,6 +213,11 @@ int ship_basePrice(Ship* s) {
   for(o = s->outfit; o != NULL; o = o->next)
     price -= o->quantity * o->data->price;
 
+  if(price < 0) {
+    WARN("Negative ship base price!");
+    price = 0;
+  }
+
   return price;
 }