parser: move atoi_n to import-divinglog.cpp

That was the only user of this helper function, so move it there.
Moreover, impelement it with the standard function std::from_chars
instead of copying the string.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/import-divinglog.cpp

@@ -16,6 +16,15 @@
 #include "membuffer.h"
 #include "gettext.h"
 
+#include <charconv>
+
+static int atoi_n(const char *ptr, size_t len)
+{
+	int res = 0;
+	std::from_chars(ptr, ptr + len, res);
+	return res;
+}
+
 static int divinglog_cylinder(void *param, int, char **data, char **)
 {
 	struct parser_state *state = (struct parser_state *)param;