[clang-tidy] Replace size comparisons with empty

Found with readability-container-size-empty

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/parser.cpp

@@ -272,7 +272,7 @@ static void print_profile(const std::vector<std::unique_ptr<profile_item_t>> &it
             my_time -= prev->parse + prev->exec;
         }
 
-        if (me->cmd.size() == 0) {
+        if (me->cmd.empty()) {
             continue;
         }