Inconsistent ordering in RGA merge method

Consider these states, assuming element 6 has a smaller timestamp than element 4 (possible if Replica B performs other operations, or has a larger DCUId) :

			     	Expected    Faulty ordering
Replica A	Replica B	(ok on A)	   on B		
 1362		 13452		 134562	  	 134526		
    1		    1		    1	  	    1		
   / \		   / \		   / \	  	   / \		
  3   2		  3   2		  3   2	  	  3   2		
   \		 /		 / \	  	 / \___	        
    6		4		4   6	  	4      6 	
		|		|	  	|		
		5		5         	5               

Note: 5 is not necessary to see the bug, but it helps understanding what should be done.

Elements are added following numbers order :

• 1, 2 and 3 are added and synchronized
• 6 is added on A, 4 and 5 on B (concurrently)
• when merging A to B, 6 is appended at the end of the array instead of being inserted after 5
• merging B to A (before or after A to B) gives the expected ordering, leading to different orderings in the two replicas.

The problem lies in RGA.mergeProtected() :

if (foundWeaker == false) { // No weaker node exist.
    index = this.nodes.size
}

This case should be handled by searching upper levels of the tree to find its next sibling.