don't re-opening index file every time setRegion is called

Author: Zilong-Li

vcfpp.h

@@ -2,7 +2,7 @@
  * @file        https://github.com/Zilong-Li/vcfpp/vcfpp.h
  * @author      Zilong Li
  * @email       [email protected]
- * @version     v0.6.1
+ * @version     v0.6.2
  * @breif       a single C++ file for manipulating VCF
  * Copyright (C) 2022-2023.The use of this code is governed by the LICENSE file.
  ******************************************************************************/
@@ -1633,6 +1633,14 @@ class BcfReader
         header.hdr = bcf_hdr_read(fp.get());
         nsamples = bcf_hdr_nsamples(header.hdr);
         SamplesName = header.getSamples();
+        if(isBcf)
+        {
+            hidx = std::shared_ptr<hts_idx_t>(bcf_index_load(fname.c_str()), details::hts_idx_close());
+        }
+        else
+        {
+            tidx = std::shared_ptr<tbx_t>(tbx_index_load(fname.c_str()), details::tabix_idx_close());
+        }
     }
 
     /** @brief set the number of threads to use */
@@ -1714,7 +1722,6 @@ class BcfReader
         // 3. if region is empty, use "."
         if(isBcf)
         {
-            hidx = std::shared_ptr<hts_idx_t>(bcf_index_load(fname.c_str()), details::hts_idx_close());
             if(itr) itr.reset(); // reset current region.
             if(region.empty())
                 itr = std::shared_ptr<hts_itr_t>(bcf_itr_querys(hidx.get(), header.hdr, "."),
@@ -1725,7 +1732,6 @@ class BcfReader
         }
         else
         {
-            tidx = std::shared_ptr<tbx_t>(tbx_index_load(fname.c_str()), details::tabix_idx_close());
             if(tidx.get() == NULL) throw std::invalid_argument(" no tabix index found!");
             if(itr) itr.reset(); // reset
             if(region.empty())