transition_region.c: check for null pointer
transition_region.c: check for null pointer

Fixes Coverity CID 709350: Dereference after null check (FORWARD_NULL)
Comparing "type" to null implies that "type" might be null.
 39        char *arg = type == NULL ? NULL : strchr( type, ':' );
...
Passing null variable "type" to function "mlt_factory_filter", which dereferences it. [show details]
 50        filter = mlt_factory_filter( profile, type, arg );

gmarco/mlt-orig,j-b-m/mlt,gmarco/mlt-orig,siddharudh/mlt,anba8005/mlt,xzhavilla/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt,gmarco/mlt-orig,xzhavilla/mlt,wideioltd/mlt,zzhhui/mlt,xzhavilla/mlt,mltframework/mlt,anba8005/mlt,mltframework/mlt,wideioltd/mlt,anba8005/mlt,gmarco/mlt-orig,gmarco/mlt-orig,wideioltd/mlt,wideioltd/mlt,wideioltd/mlt,siddharudh/mlt,xzhavilla/mlt,xzhavilla/mlt,anba8005/mlt,zzhhui/mlt,gmarco/mlt-orig,zzhhui/mlt,zzhhui/mlt,siddharudh/mlt,gmarco/mlt-orig,xzhavilla/mlt,siddharudh/mlt,zzhhui/mlt,siddharudh/mlt,siddharudh/mlt,mltframework/mlt,xzhavilla/mlt,mltframework/mlt,xzhavilla/mlt,wideioltd/mlt,anba8005/mlt,zzhhui/mlt,wideioltd/mlt,anba8005/mlt,siddharudh/mlt,mltframework/mlt,gmarco/mlt-orig,zzhhui/mlt,wideioltd/mlt,gmarco/mlt-orig,zzhhui/mlt,anba8005/mlt,siddharudh/mlt,mltframework/mlt,j-b-m/mlt,xzhavilla/mlt,j-b-m/mlt,mltframework/mlt,anba8005/mlt,mltframework/mlt,j-b-m/mlt,wideioltd/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,zzhhui/mlt,j-b-m/mlt,anba8005/mlt,siddharudh/mlt,j-b-m/mlt