Avoid row map corruption when replacing a subset of a fold's buffer rows

Fixes #1576

When splicing regions into the row map, we always express the starting
buffer row, then the number of buffer rows covered by the regions we're
inserting. When we're inserting regions representing folds, they always
extend to the end of a fold, so we need to ensure the endBufferRow also
extends to the end of the fold.

For example, say rows [5…10] are folded, and we handle a replacement of
rows [5…8]. We will still insert a region for the fold covering 1 screen
row and 5 buffer rows, so we need to update the endBufferRow to extend
to the end of the fold as well (10).

src/display-buffer.coffee

@@ -584,6 +584,7 @@ class DisplayBuffer extends Model
 
   updateScreenLines: (startBufferRow, endBufferRow, bufferDelta=0, options={}) ->
     startBufferRow = @rowMap.bufferRowRangeForBufferRow(startBufferRow)[0]
+    endBufferRow = @rowMap.bufferRowRangeForBufferRow(endBufferRow - 1)[1]
     startScreenRow = @rowMap.screenRowRangeForBufferRow(startBufferRow)[0]
     endScreenRow = @rowMap.screenRowRangeForBufferRow(endBufferRow - 1)[1]