Label button 'Start call' if none is in progress yet, fix #976
Label button 'Start call' if none is in progress yet, fix #976

Signed-off-by: Jan-Christoph Borchardt <7f550a9f4c44173a37664d938f1355f0f92a47a7@jancborchardt.net>

nextcloud/spreed,nextcloud/spreed,nextcloud/spreed