Suppress Safari promise rejections.

Currently Webkit implements createImageBitmap() but returns a promise
rejection.

Note that once Webkit implements createImageBitmap() correctly these
changes should be removed.

src/shared/atlas/CharAtlasGenerator.ts

@@ -6,7 +6,7 @@
 import { FontWeight } from 'xterm';
 import { CHAR_ATLAS_CELL_SPACING, ICharAtlasConfig } from './Types';
 import { IColor } from '../Types';
-import { isFirefox } from '../utils/Browser';
+import { isFirefox, isSafari } from '../utils/Browser';
 
 declare const Promise: any;
 
@@ -99,7 +99,7 @@ export function generateStaticCharAtlasTexture(context: Window, canvasFactory: (
   // if support is lacking as drawImage works there too. Firefox is also
   // included here as ImageBitmap appears both buggy and has horrible
   // performance (tested on v55).
-  if (!('createImageBitmap' in context) || isFirefox) {
+  if (!('createImageBitmap' in context) || isFirefox || isSafari) {
     // Don't attempt to clear background colors if createImageBitmap is not supported
     if (canvas instanceof HTMLCanvasElement) {
       // Just return the HTMLCanvas if it's a HTMLCanvasElement