Fix UB in count_caches() causing crash in some cases

common.cpp

@@ -315,7 +315,7 @@ int count_caches(const Caches& cc, std::string& codes, std::function<bool(const
 			codes += ' ';
 		}
 	}
-	codes.pop_back();
+	if (!codes.empty()) codes.pop_back();
 	return count;
 }