Yes, near the beginning of this chapter Thorin does say:
That stone of all in the treasure I name unto myself, and I will be avenged on anyone who finds it and withholds it.
But this is not a curse, only a threat. Thorin does not say, “cursed be anyone who finds it and withholds it!” This may be because Tolkien does not wish to bring any suggestion of a curse into this tale because in genuine folktales and traditional tales curses and pronounced fates often have dread effect, and give many tales their power. It would be a cheat to the reader who would expect anything presented as a curse to eventually take effect, or at least take partial effect and the tale then perhaps turn to how the cursed person manages to get out of it.
This brings up the question of why Thorin doesn’t pronounce a curse on the possible thief. Cursing worked for Mîm the Petty-dwarf against Andróg in
The Children of Húrin and
Unfinished Tales.
Perhaps the reader must accept that cursing only works in Tolkien’s tales when the curser is, perhaps momentarily, foresighted and that there are thousands of empty curses not mentioned in the tales that just don’t take effect. Sauron (and Saruman and Denethor and Gollum) might just have pronounced, ″I curse anyone who finds the One Ring or otherwise obtains it (except for myself) to do all in his (or her or its) power to bring the Ring to me or do whatever seems best to further this!” But then Elrond and Gandalf might have pronounced, “I curse anyone who finds the One Ring or otherwise obtains it to cast the Ring into Mount Doom or do whatever seems best to further this!” Of course good people would have to add a rider, something like, “if this be according to his (or her or its) will and may the Valar and/or Eru use what powers they are allowed to persuade him (or her or it)!”
The conversation between Bilbo with the Elvenking and Bard is most enjoyable, with Bilbo speaking informally in modern idiom and the other two responding in high and formal and somewhat staid translation talk. Tolkien must have much enjoyed writing this as he must have enjoyed the chance to do it again with Merry and Pippin meeting King Théoden. This works so well because Tolkien avoids doing it often.
Tolkien never explains the coincidence that Bilbo and his escort just happen to pass by the tent which is hiding Gandalf and what Gandalf is doing there nor why neither the Elvenking nor Bard saw fit to summon Gandalf when Bilbo appeared, assuming the Elvenking and Bard knew that Gandalf was in the camp. It is reasonable to assume that the Elvenking and Bard had previously welcomed Gandalf when he appeared and had assigned him that tent.