Changed "-o -" to be treated as -c.

Writing to stdout has some special handling.  Instead of having -o handle writing to stout, use the existing -c code.

bgzip.c

@@ -297,9 +297,15 @@ int main(int argc, char **argv)
         return 1;
     }
 
-    if (write_fname && pstdout) {
-        fprintf(stderr, "[bgzip] Cannot write to %s and stdout at the same time.\n", write_fname);
-        return 1;
+    if (write_fname) {
+        if (pstdout) {
+            fprintf(stderr, "[bgzip] Cannot write to %s and stdout at the same time.\n", write_fname);
+            return 1;
+        } else if (strncmp(write_fname, "-", strlen(write_fname)) == 0) {
+            // stdout has special handling so treat as -c
+            pstdout = 1;
+            write_fname = NULL;
+        }
     }
 
     do {