fix: string_replace_at check args validity

src/string.c

@@ -62,6 +62,10 @@ char *string_replace_at(const char *src, unsigned int from, unsigned int to,
   unsigned long rpl_len;
   char *dst;
 
+  if (to < from) {
+    return "";
+  }
+
   src_len = strnlen(src, STR_LEN * STR_LEN);
   rpl_len = strnlen(rpl, STR_LEN * STR_LEN);