views: validate client partitions in /action/software

Redirect the user when /action/software is accessed on a client
without valid partitions.

ogcp/views.py

@@ -1199,6 +1199,11 @@ def action_software():
                  f"| {PART_TYPE_CODES.get(part.get('code'), 'UNKNOWN')} "
                  f"{FS_CODES.get(part.get('filesystem'), 'UNKNOWN')}")
             )
+
+        if not form.os.choices:
+            flash(_(f'No valid partition available'), category='error')
+            return redirect(url_for('commands'))
+
     return render_template('actions/software.html', form=form, scopes=scopes)
 
 @app.route('/action/session', methods=['GET', 'POST'])