Sanity check for trail

geostat.cpp

@@ -311,9 +311,13 @@ int main(int argc, char** argv) {
 			std::exit(EXIT_FAILURE);
 		}
 		Heat hmap(chosen_map);
-		if (trail)
+		if (trail) {
+			if (sorted_fcaches.size() < 2) {
+				std::cout << "You need at least 2 caches for a trail.\n";
+				std::exit(EXIT_FAILURE);
+			}
 			hmap.generate_path(heat_file, sorted_fcaches);
-		else
+		} else
 			hmap.generate(heat_file, fcc, heat_stamp_size, (heat_exp == 1 ? "exp" : "soft"));
 		std::cout << "<img class=\"heatmap\" src=\"" << heat_file << "\" alt=\"heat map\">\n";
 	}