Fix grid card size when square (#9056)

gallery/src/demos/demo-hui-grid-and-stack-card.ts

@@ -143,6 +143,15 @@ const CONFIGS = [
     entity: light.kitchen_lights
     `,
   },
+  {
+    heading: "Size for single card",
+    config: `
+- type: grid
+  cards:
+  - type: entity
+    entity: light.kitchen_lights
+    `,
+  },
 
   {
     heading: "Vertical Stack",

src/panels/lovelace/cards/hui-grid-card.ts

@@ -25,7 +25,9 @@ class HuiGridCard extends HuiStackCard<GridCardConfig> {
     if (this.square) {
       const rowHeight = SQUARE_ROW_HEIGHTS_BY_COLUMNS[this.columns] || 1;
       return (
-        (this._cards.length / this.columns) * rowHeight +
+        (this._cards.length < this.columns
+          ? rowHeight
+          : (this._cards.length / this.columns) * rowHeight) +
         (this._config.title ? 1 : 0)
       );
     }