Don't accidentally reattach coconuts (#1858)

I'm not sure how exactly that issue happens, but in the attached video
it looks like C4D_StaticBack was accidentally set again. As the XOR
operation can do that, I'm changing it to always set the C4D_StaticBack
bit to 0.

planet/Objects.ocd/Vegetation.ocd/Trees.ocd/Coconut.ocd/CoconutSeed.ocd/Script.c

@@ -25,7 +25,7 @@ public func AttachToTree(object tree)
 public func DetachFromTree(bool no_bounce)
 {
 	ClearScheduleCall(this, "DetachFromTree");
-	SetCategory(GetCategory() ^ C4D_StaticBack);
+	SetCategory(GetCategory() & (~C4D_StaticBack));
 	SetXDir(Random(3)-1);
 	if (mother) mother->LostCoconut();
 	mother = nil;