fix(material-experimental/chips): fix empty check when no chips (#20025)

* fix(material-experimental/chips): fix empty check when no chips

* same for chipset

* check for input too

Author: andrewseguin

src/material-experimental/mdc-chips/chip-grid.ts

@@ -154,7 +154,10 @@ export class MatChipGrid extends _MatChipGridMixinBase implements AfterContentIn
    * Implemented as part of MatFormFieldControl.
    * @docs-private
    */
-  get empty(): boolean { return this._chipInput.empty && this._chips.length === 0; }
+  get empty(): boolean {
+    return (!this._chipInput || this._chipInput.empty) &&
+        (!this._chips || this._chips.length === 0);
+  }
 
     /** The ARIA role applied to the chip grid. */
   get role(): string | null { return this.empty ? null : 'grid'; }

src/material-experimental/mdc-chips/chip-set.ts

@@ -193,7 +193,7 @@ export class MatChipSet extends _MatChipSetMixinBase implements AfterContentInit
 
   /** Checks whether any of the chips is focused. */
   protected _hasFocusedChip() {
-    return this._chips.some(chip => chip._hasFocus);
+    return this._chips && this._chips.some(chip => chip._hasFocus);
   }
 
   /** Syncs the chip-set's state with the individual chips. */