Address code review comments.

sam.c

@@ -3220,8 +3220,10 @@ int sam_format1(const bam_hdr_t *h, const bam1_t *b, kstring_t *str)
 // reference count the structure.
 int sam_write1(htsFile *fp, const sam_hdr_t *hdr, const bam1_t *b)
 {
-    const sam_hdr_t *h = hdr;
-    if (!h) h = fp->bam_header;
+    if (!fp || !b) { errno = EINVAL; return -1; }
+    const sam_hdr_t *h = hdr ? hdr : fp->bam_header;
+    if (!h) { hts_log_error("No header available for file \"%s\"", fp->fn); return -1; }
+
     switch (fp->format.format) {
     case binary_format:
         fp->format.category = sequence_data;

vcf.c

@@ -3291,8 +3291,6 @@ static int vcf_idx_init(htsFile *fp, bcf_hdr_t *h, int min_shift, const char *fn
     u32_to_le(0,       conf+20); // n.skip
     u32_to_le(0,       conf+24); // ref name len
     if (hts_idx_set_meta(fp->idx, sizeof(conf)*sizeof(*conf), (uint8_t *)conf, 1) < 0) {
-        hts_idx_destroy(fp->idx);
-        fp->idx = NULL;
         return -1;
     }
     fp->fnidx = strdup(fnidx);