merge.js in codemirror-rails-5.12

- old
+ new

@@ -425,11 +425,12 @@
     }
   }
 
   function copyChunk(dv, to, from, chunk) {
     if (dv.diffOutOfDate) return;
+    var start = chunk.editTo > to.lastLine() ? Pos(chunk.editFrom - 1) : Pos(chunk.editFrom, 0)
     to.replaceRange(from.getRange(Pos(chunk.origFrom, 0), Pos(chunk.origTo, 0)),
-                         Pos(chunk.editFrom, 0), Pos(chunk.editTo, 0));
+                    start, Pos(chunk.editTo, 0));
   }
 
   // Merge view, containing 0, 1, or 2 diff views.
 
   var MergeView = CodeMirror.MergeView = function(node, options) {