Fix compositions disappear after reopening project with locked track.

BUG: 412369
1 job for Applications/19.08 in 3 minutes and 4 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
failed linux stable-kf5-qt5 qt5.12 #20345

00:03:04

 
Name Stage Failure
failed
linux stable-kf5-qt5 qt5.12 Build
[  2%] Built target kiss_fft
[ 3%] Linking CXX shared module mltpreview.so
[ 2%] Built target doc-index-cache-bz2
[ 3%] Built target mltpreview
make: *** [Makefile:141: all] Error 2
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1