Backport of "Fix leaks and minor races in GES and debugging statements" into 1.20
Backport of !3428 (merged) "Fix leaks and minor races in GES and debugging statemtns".
Commits:
- 137d38c9 ges-launch: Don't leak help string
- 40d98583 ges-structure-parser: Don't leak failed strings
- ba5beb55 ges-project: Don't leak string
- 4aaaf297 ges-xml-formatter: Plug some leaks
- 615fbb3f ges-demux: Don't leak string
- 5a08b220 ges-launcher: Don't leak string
- 845dcf7e imagesequencesrc: Don't leak caps
- db2146d0 decodebin2: Minor debug fix for decodepad