Guard against missing first size

Author: noisysocks

packages/components/src/font-size-picker/index.tsx

@@ -156,7 +156,7 @@ const UnforwardedFontSizePicker = (
 	// operates in a legacy "unitless" mode where UnitControl can only be used
 	// to select px values and onChange() is always called with number values.
 	const hasUnits =
-		typeof value === 'string' || typeof fontSizes[ 0 ].size === 'string';
+		typeof value === 'string' || typeof fontSizes[ 0 ]?.size === 'string';
 
 	const [ valueNumber, valueUnit ] = parseNumberAndUnitFromSize( value );
 	const isValueUnitRelative =