(ml5717) Fixed interval union in drawing-crdt

@im2517 Please have a look at the interval union function - but testing seems to suggest it works now

src/drawing-crdt

-Subproject commit dc2b67f607a53b0ecb761260916376e275d3d62e
+Subproject commit 3dd0a1fa0b2ac0d9fd331659b526a91419821714