flux-mini: fix bulksubmit error on zero jobs

Problem: when zero jobs are given to bulksubmit, it fails with a
ZeroDivisionError when printing the progress bar, or (if no
progress bar) it fails because self.flux_handle was not
initialized.

Solution: check for zero jobs and throw a reasonable error.

Author: jameshcorbett

src/cmd/flux-mini.py

@@ -1374,6 +1374,8 @@ def main(self, args):
         for xargs in commands:
             total += len(self.cc_list(xargs))
 
+        if total == 0:
+            raise ValueError("no jobs provided for bulk submission")
         #  Initialize progress bar if requested:
         if args.progress:
             if not args.dry_run: