avoids -I with multiple inputs on index/reindex

bgzip.1

@@ -54,9 +54,7 @@ bgzip \- Block compression/decompression utility
 .IR size ]
 .RB [ -@
 .IR threads ]
-.RI [ file1 ]
-.RI [ file2 ]
-.RI [ ... ]
+.RI [[ file1 ][...]]
 .PP
 .SH DESCRIPTION
 .PP

bgzip.c

@@ -199,6 +199,12 @@ int main(int argc, char **argv)
         fprintf(stderr, "[bgzip] Index file name expected with rebgzip.  See -I option.\n");
         return 1;
     }
+    /* avoid -I / indexfile with multiple inputs while index/reindex. these wont be set during
+    read/decompress and are not considered even if set */
+    if ( (index || reindex) && index_fname && argc - optind > 1) {
+        fprintf(stderr, "[bgzip] Cannot specify index filename with multiple data file on index, reindex.\n");
+        return 1;
+    }
 
     do {
         isstdin = optind >= argc ? 1 : !strcmp("-", argv[optind]);          //using stdin or not?
@@ -224,7 +230,7 @@ int main(int argc, char **argv)
                 return 1;
             }
 
-            if ( argc>optind && !isstdin )
+            if ( argc>optind && !isstdin )                  //named input file that isn't an explicit "-"
             {
                 if (pstdout)
                     fp = bgzf_open("-", out_mode);