Handle input errors for --indent

Handle malformed and overflowing arguments. Also, forbid leading and
trailing spaces to match the behavior of tonumber from commit ce0e788
(improve tonumber/0 performance by parsing input as number literal,
2024-03-02).

Author: thaliaarchi

src/main.c

@@ -453,12 +453,15 @@ int main(int argc, char* argv[]) {
           fprintf(stderr, "%s: --indent takes one parameter\n", progname);
           die();
         }
-        dumpopts &= ~(JV_PRINT_TAB | JV_PRINT_INDENT_FLAGS(7));
-        int indent = atoi(argv[i+1]);
-        if (indent < -1 || indent > 7) {
+        char* end = NULL;
+        errno = 0;
+        long indent = strtol(argv[i+1], &end, 10);
+        if (errno || indent < -1 || indent > 7 ||
+            isspace(*argv[i+1]) || end == NULL || *end) {
           fprintf(stderr, "%s: --indent takes a number between -1 and 7\n", progname);
           die();
         }
+        dumpopts &= ~(JV_PRINT_TAB | JV_PRINT_INDENT_FLAGS(7));
         dumpopts |= JV_PRINT_INDENT_FLAGS(indent);
         i++;
         continue;