🔥 Remove screen delta guards

Screen delta represents the differences in number of lines between the
version before the change and the version after the change.
Changes that comes from the TextEditor always have a screen delta. The
only ones that doesn’t comes from the decoration management. And in
fact, manipulating decorations doesn’t changes the screen lines so
their screen delta is always 0.

lib/mixins/canvas-drawer.coffee

@@ -423,9 +423,6 @@ class CanvasDrawer extends Mixin
     for change in @pendingChanges
       newIntactRanges = []
       for range in intactRanges
-        if isNaN(change.screenDelta)
-          change.screenDelta = change.end - change.start
-
         if change.end < range.start and change.screenDelta != 0
           newIntactRanges.push(
             start: range.start + change.screenDelta

lib/mixins/decoration-management.coffee

@@ -198,7 +198,7 @@ class DecorationManagement extends Mixin
 
       [start, end] = [end, start] if start.row > end.row
 
-      @emitRangeChanges({start, end, screenDelta: end - start})
+      @emitRangeChanges({start, end})
 
     decoration = new Decoration(marker, this, decorationParams)
     @decorationsByMarkerId[marker.id] ?= []
@@ -229,14 +229,12 @@ class DecorationManagement extends Mixin
   # Internal: Emits a change for the specified range.
   #
   # range - The `Range` to emits changes for.
-  emitRangeChanges: (range) ->
+  emitRangeChanges: (range, screenDelta) ->
     startScreenRow = range.start.row
     endScreenRow = range.end.row
     lastRenderedScreenRow  = @getLastVisibleScreenRow()
     firstRenderedScreenRow = @getFirstVisibleScreenRow()
-    screenDelta = (lastRenderedScreenRow - firstRenderedScreenRow) - (endScreenRow - startScreenRow)
-
-    screenDelta = 0 if isNaN(screenDelta)
+    screenDelta ?= (lastRenderedScreenRow - firstRenderedScreenRow) - (endScreenRow - startScreenRow)
 
     changeEvent =
       start: startScreenRow