fix for incorrect failure message with invalid reference file and nul…

…l check

hts.c

@@ -922,6 +922,7 @@ htsFile *hts_open_format(const char *fn, const char *mode, const htsFormat *fmt)
         fn = rmme;
     }
 
+    errno = 0;      //reset to ensure appropriate error display
     hfile = hopen(fn, smode);
     if (hfile == NULL) goto error;
 
@@ -938,10 +939,19 @@ htsFile *hts_open_format(const char *fn, const char *mode, const htsFormat *fmt)
          fmt->format == fastq_format))
         fp->format.format = fmt->format;
 
-    if (fmt && fmt->specific)
-        if (hts_opt_apply(fp, fmt->specific) != 0)
+    if (fmt && fmt->specific) {
+        int save_errno = errno;
+        if (hts_opt_apply(fp, fmt->specific) != 0) {
+            if (((hts_opt*)fmt->specific)->opt == CRAM_OPT_REFERENCE) {
+                const char *ref = ((hts_opt*)fmt->specific)->val.s;
+                hts_log_error("Couldn't load reference \"%s\" : %s",
+                    ref ? ref : "(NULL)", strerror(errno));
+                // set error to error prior to reference file operation
+                errno = save_errno;
+            }
             goto error;
-
+        }
+    }
     if ( rmme ) free(rmme);
     return fp;
 
@@ -1595,6 +1605,10 @@ htsFile *hts_hopen(hFILE *hfile, const char *fn, const char *mode)
 int hts_close(htsFile *fp)
 {
     int ret = 0, save;
+    if (!fp) {
+        errno = EINVAL;
+        return -1;
+    }
 
     switch (fp->format.format) {
     case binary_format: