graph: fix null check lost in last merge

rhodecode/public/js/graph.js

@@ -68,6 +68,8 b' function BranchRenderer() {'
 			this.scale(scale);
 
 			var row = document.getElementById("chg_"+idx);
+			if (row == null)
+				continue;
 			var	next = document.getElementById("chg_"+(idx+1));
 			var extra = 0;