tile.canvas is always true after a successful _ensureContext(tile)

_applyDelta returns early if the initial "ensureContext" of the tile
fails.

i.e.

  var ctx = this._ensureContext(tile);
  if (!ctx) // out of canvas / texture memory.
    return;

and ensureContext already calls ensureCanvas, so tile.canvas is
always true in the remainder of this function.

The "defer constructing the image & applying these deltas until the tile
is rendered via ensureCanvas." implied a sort of deliberate optimization
to wait until render time to apply the delta which doesn't actually
exist.

Also move the stray "// 'Uint8Array' delta" comment back to where it
originally came from as documentation of the type of the param, as in

commit 4140bf8741
Date:   Sat Nov 6 11:11:13 2021 +0000

    Bring back the delta application JS from the 6.4 branch.

...

 _applyDelta: function(tile, delta) {
         // 'Uint8Array' delta

...

Signed-off-by: Caolán McNamara <caolan.mcnamara@collabora.com>
Change-Id: If15a897c3251f28639c9f1112687e543421e457d

browser/src/layer/tile/CanvasTileLayer.js

@@ -6738,6 +6738,8 @@ L.CanvasTileLayer = L.Layer.extend({
 	},
 
 	_applyDelta: function(tile, rawDelta, isKeyframe, wireMessage) {
+		// 'Uint8Array' rawDelta
+
 		if (this._debugDeltas)
 			window.app.console.log('Applying a raw ' + (isKeyframe ? 'keyframe' : 'delta') +
 					       ' of length ' + rawDelta.length +
@@ -6803,14 +6805,6 @@ L.CanvasTileLayer = L.Layer.extend({
 			tile.rawDeltas = tmp;
 		}
 
-		// 'Uint8Array' delta
-		if (!tile.canvas)
-		{
-			// defer constructing the image & applying these deltas
-			// until the tile is rendered via ensureCanvas.
-			return;
-		}
-
 		// apply potentially several deltas in turn.
 		var i = 0;
 		var offset = 0;