[media] fixed rendition when crop is not set
[media] fixed rendition when crop is not set

rendition was wailing is crop was having empty string for "width" or
"height" key, this commit fix it

SDTS-24

superdesk/superdesk-core,ioanpocol/superdesk-core,hlmnrmr/superdesk-core,petrjasek/superdesk-core,superdesk/superdesk-core,superdesk/superdesk-core,ioanpocol/superdesk-core,petrjasek/superdesk-core,marwoodandrew/superdesk-core,petrjasek/superdesk-core,mdhaman/superdesk-core,mugurrus/superdesk-core,nistormihai/superdesk-core,mdhaman/superdesk-core,ioanpocol/superdesk-core,mugurrus/superdesk-core,mdhaman/superdesk-core,petrjasek/superdesk-core,hlmnrmr/superdesk-core,nistormihai/superdesk-core,marwoodandrew/superdesk-core,mugurrus/superdesk-core,superdesk/superdesk-core