Fix \u259B rendering

Fixes xtermjs#3902

Author: Tyriar

src/browser/renderer/CustomGlyphs.ts

@@ -42,7 +42,7 @@ export const blockElementDefinitions: { [index: string]: IBlockVector[] | undefi
   '▘': [{ x: 0, y: 0, w: 4, h: 4 }],                             // QUADRANT UPPER LEFT
   '▙': [{ x: 0, y: 0, w: 4, h: 8 }, { x: 0, y: 4, w: 8, h: 4 }], // QUADRANT UPPER LEFT AND LOWER LEFT AND LOWER RIGHT
   '▚': [{ x: 0, y: 0, w: 4, h: 4 }, { x: 4, y: 4, w: 4, h: 4 }], // QUADRANT UPPER LEFT AND LOWER RIGHT
-  '▛': [{ x: 0, y: 0, w: 4, h: 8 }, { x: 0, y: 0, w: 4, h: 8 }], // QUADRANT UPPER LEFT AND UPPER RIGHT AND LOWER LEFT
+  '▛': [{ x: 0, y: 0, w: 4, h: 8 }, { x: 4, y: 0, w: 4, h: 4 }], // QUADRANT UPPER LEFT AND UPPER RIGHT AND LOWER LEFT
   '▜': [{ x: 0, y: 0, w: 8, h: 4 }, { x: 4, y: 0, w: 4, h: 8 }], // QUADRANT UPPER LEFT AND UPPER RIGHT AND LOWER RIGHT
   '▝': [{ x: 4, y: 0, w: 4, h: 4 }],                             // QUADRANT UPPER RIGHT
   '▞': [{ x: 4, y: 0, w: 4, h: 4 }, { x: 0, y: 4, w: 4, h: 4 }], // QUADRANT UPPER RIGHT AND LOWER LEFT